         COUR INTERNATIONALE DE JUSTICE

             RECUEIL DES ARRÊTS,
      AVIS CONSULTATIFS ET ORDONNANCES

 EFFETS JURIDIQUES DE LA SÉPARATION
      DE L’ARCHIPEL DES CHAGOS
          DE MAURICE EN 1965

      AVIS CONSULTATIF DU 25 FÉVRIER 2019

                2019
         INTERNATIONAL COURT OF JUSTICE

           REPORTS OF JUDGMENTS,
        ADVISORY OPINIONS AND ORDERS

LEGAL CONSEQUENCES OF THE SEPARATION
     OF THE CHAGOS ARCHIPELAGO
        FROM MAURITIUS IN 1965

     ADVISORY OPINION OF 25 FEBRUARY 2019

                          Mode oﬃciel de citation :
   Effets juridiques de la séparation de l’archipel des Chagos de Maurice
             en 1965, avis consultatif, C.I.J. Recueil 2019, p. 95

                             Oﬃcial citation :
   Legal Consequences of the Separation of the Chagos Archipelago from
      Mauritius in 1965, Advisory Opinion, I.C.J. Reports 2019, p. 95

                                             No de vente:
ISSN 0074-4441
ISBN 978-92-1-157366-4
                                             Sales number   1164

                              25 FÉVRIER 2019

                             AVIS CONSULTATIF

 EFFETS JURIDIQUES DE LA SÉPARATION
      DE L’ARCHIPEL DES CHAGOS
          DE MAURICE EN 1965

LEGAL CONSEQUENCES OF THE SEPARATION
     OF THE CHAGOS ARCHIPELAGO
        FROM MAURITIUS IN 1965

                             25 FEBRUARY 2019

                            ADVISORY OPINION

                                                                              95

                        TABLE OF CONTENTS

                                                                       Paragraphs
Chronology of the Procedure                                                 1-24
 I. Events Leading to the Adoption of the Request for the
    Advisory Opinion                                                       25-53
 II. Jurisdiction and Discretion                                           54-91
    A. Jurisdiction                                                        55-62
    B. Discretion                                                          63-68
       1. Whether advisory proceedings are suitable for determina-
          tion of complex and disputed factual issues                      69-74

       2. Whether the Court’s response would assist the General
          Assembly in the performance of its functions                     75-78
       3. Whether it would be appropriate for the Court to
          re-examine a question allegedly settled by the Arbitral
          Tribunal constituted under UNCLOS Annex VII in the
          Arbitration regarding the Chagos Marine Protected Area           79-82

       4. Whether the questions asked relate to a pending dispute
          between two States, which have not consented to its
          settlement by the Court                                          83-91
III. The Factual Context of the Separation of the Chagos
     Archipelago from Mauritius                                           92-131
    A. The discussions between the United Kingdom and the
       United States with respect to the Chagos Archipelago                94-97
    B. The discussions between the Government of the United
       Kingdom and the representatives of the colony of Mauritius
       with respect to the Chagos Archipelago                             98-112
    C. The situation of the Chagossians                                  113-131
IV. The Questions Put to the Court by the General Assembly               132-182
    A. Whether the process of decolonization of Mauritius was
       lawfully completed having regard to international law
       (Question (a))                                                    139-174
       1. The relevant period of time for the purpose of identifying
          the applicable rules of international law                      140-143
       2. Applicable international law                                   144-162
       3. The functions of the General Assembly with regard to
          decolonization                                                 163-169
       4. Application in the present proceedings                         170-174

                                                                               4

            separation of the chagos (advisory opinion)                96

    B. The consequences under international law arising from the
       continued administration by the United Kingdom of the
       Chagos Archipelago (Question (b))                           175-182
Operative Clause                                                      183

                                                                        5

                                                                               97

               INTERNATIONAL COURT OF JUSTICE

                                  YEAR 2019                                              2019
                                                                                25 February
                                                                                General List
                               25 February 2019                                        No. 169

LEGAL CONSEQUENCES OF THE SEPARATION
     OF THE CHAGOS ARCHIPELAGO
        FROM MAURITIUS IN 1965

   Events leading to the adoption of General Assembly resolution 71/292 requesting
an advisory opinion.
   Geographic location of Mauritius in the Indian Ocean — Chagos Archipelago,
including the island of Diego Garcia, administered by the United Kingdom during
colonization as a dependency of Mauritius — Adoption on 14 December 1960 of
the Declaration on the Granting of Independence to Colonial Countries and Peo-
ples (General Assembly resolution 1514 (XV)) —Establishment of the Special
Committee on Decolonization (“Committee of Twenty-Four”) to monitor the
implementation of resolution 1514 (XV) — Lancaster House agreement between
the representatives of the colony of Mauritius and the United Kingdom Govern-
ment regarding the detachment of the Chagos Archipelago from Mauritius — Cre-
ation of the British Indian Ocean Territory (“BIOT”), including the Chagos
Archipelago — Agreement between the United States of America and the
United Kingdom concerning the availability of the BIOT for defence purposes —
Adoption by the General Assembly of resolutions on the territorial integrity of
non-self-governing territories — Independence of Mauritius — Forcible removal of
the population of the Chagos Archipelago — Request by Mauritius for the BIOT
to be disbanded and the territory restored to it — Creation of a marine protected
area around the Chagos Archipelago by the United Kingdom — Challenge to the
creation of a marine protected area by Mauritius before an Arbitral Tribunal and
decision of the Tribunal.

                                       * *
   Jurisdiction of the Court to give the advisory opinion requested.
   Article 65, paragraph 1, of the Statute — Article 96, paragraph 1, of the Char-
ter — Competence of the General Assembly to seek advisory opinions — Request
made in accordance with the Charter — Questions submitted to the Court are legal
in character.

                                                                                6

              separation of the chagos (advisory opinion)                         98

   Argument that there is no exact statement of the question upon which an opinion
is required — Any lack of clarity in the questions cannot deprive the Court of its
jurisdiction — Arguments examined by the Court when it analyses the questions
put by the General Assembly.
   The Court has jurisdiction to give the advisory opinion requested.

                                        * *
   Discretion of the Court to decide whether it should give an opinion.
   Integrity of the Court’s judicial function — Only “compelling reasons” may
lead the Court to refuse to exercise its judicial function.
   Argument that advisory proceedings are not suitable for determination of com-
plex and disputed factual issues — Sufficient information on the facts at the dis-
posal of the Court.
   Argument that the Court’s response would not assist the General Assembly in
the performance of its functions — Determination of the usefulness of the opinion
left to the requesting organ.
   Argument that an advisory opinion by the Court would reopen the findings of an
Arbitral Tribunal — Opinion given to the General Assembly, not to States —
Principle of res judicata does not preclude the rendering of an advisory opinion —
Issues determined by the Arbitral Tribunal not the same as those before the Court.

   Argument that the questions asked relate to a pending territorial dispute between
two States, which have not consented to its settlement by the Court — Questions
relate to the decolonization of Mauritius — Active role played by the General
Assembly with regard to decolonization — Issues raised by the request located in
the broader frame of reference of decolonization — The Court not dealing with a
bilateral dispute by giving an opinion on legal issues on which divergent views are
said to have been expressed by the two States — Giving the opinion requested does
not have the effect of circumventing the principle of consent by a State to the judi-
cial settlement of its dispute with another State.

   No compelling reasons for the Court to decline to give the opinion requested by
the General Assembly.

                                        * *
   Factual context of the separation of the Chagos Archipelago from Mauritius
and the removal of Chagossians from the archipelago.
   Discussions between the United Kingdom and the United States on the use of
certain British-owned islands in the Indian Ocean for defence purposes — Agree-
ment between the two parties for the establishment of a military base by the
United States on the island of Diego Garcia.
   Discussions between the Government of the United Kingdom and the representa-
tives of the colony of Mauritius with respect to the Chagos Archipelago — Fourth
Constitutional Conference held in London in September 1965 involving representa-
tives of the two parties — Lancaster House agreement — Agreement in principle
by representatives of the colony of Mauritius to the detachment of the Chagos
Archipelago from the territory of Mauritius.
   Situation of the Chagossians — Entire population of Chagos Archipelago for-
cibly removed from the territory between 1967 and 1973 and prevented from return-

                                                                                7

              separation of the chagos (advisory opinion)                         99

ing — Compensation paid by the United Kingdom to certain Chagossians — Var-
ious proceedings initiated by Chagossians before United Kingdom courts, the
European Court of Human Rights and the Human Rights Committee — Commit-
tee’s recommendations that Chagossians should be able to exercise their right to
return to their territory — Today Chagossians are dispersed in several countries,
including the United Kingdom, Mauritius and Seychelles — By virtue of
United Kingdom law and judicial decisions of that country, they are not allowed to
return to the archipelago.

                                        * *
   Language of the questions posed in resolution 71/292 — Competence of the
Court to clarify the questions put to it for an advisory opinion — No need to refor-
mulate the questions in this instance — No need for the Court to interpret restric-
tively the questions put by the General Assembly.

                                        * *
   Question of whether the process of decolonization of Mauritius was lawfully
completed having regard to international law.
   Relevant period and applicable rules of law.
   Relevant period between the separation of the Chagos Archipelago in 1965 and
the independence of Mauritius in 1968 — Evolution of the law on self-determina-
tion — Right to self-determination has a broad scope of application as a funda-
mental human right — In these proceedings, the Court only to analyse that right
in the context of decolonization — Right to self-determination enshrined by the
Charter and reaffirmed by subsequent General Assembly resolutions — Resolu-
tion 1514 (XV) represents a defining moment in the consolidation of State prac-
tice on decolonization — Declaratory character of resolution 1514 (XV) with
regard to the right to self-determination as a customary norm — Resolu-
tion 1514 (XV) provides that any disruption of the national unity and territorial
integrity of a country is incompatible with the purposes and principles of the Char-
ter — Reaffirmation of the right of all peoples to self-determination by the Inter-
national Covenants on Civil and Political Rights and on Economic, Social and
Cultural Rights — Right to self-determination reiterated in the Declaration on
Principles of International Law concerning Friendly Relations and Co-operation
among States —Means of implementing the right to self-determination in a
non-self-governing territory set out in resolution 1541 (XV) — Exercise of
self-determination must be the expression of the free and genuine will of the people
concerned — Right to self-determination, under customary international law, does
not impose a specific mechanism for its implementation in all instances — Right to
self-determination of a people defined by reference to the entirety of a non-self-
governing territory — Customary law character of the right to territorial integrity
of a non-self-governing territory as a corollary of the right to self-determination —
Incompatibility with the right to self-determination of any detachment by the
administering Power of part of a non-self-governing territory, unless such detach-
ment is based on the freely expressed and genuine will of the people of the territory
concerned.
   Right to self-determination, as a customary norm, constitutes the applicable
international law during the relevant period.

                                                                                8

              separation of the chagos (advisory opinion)                      100

   Functions of the General Assembly with regard to decolonization.
   Crucial role of the General Assembly with regard to decolonization — Moni-
toring of the means by which the free and genuine will of the people of a non-self-
governing territory is expressed — General Assembly has consistently called
upon administering Powers to respect the territorial integrity of non-self-governing
territories.
   Examination of the circumstances relating to the detachment of the Chagos
Archipelago and its accordance with the applicable international law.
   Agreement in principle of the Council of Ministers of Mauritius to the detach-
ment of the Chagos Archipelago given when the colony of Mauritius was under the
authority of the United Kingdom, its administering Power — Agreement not an
international agreement — No free and genuine expression of the will of the peo-
ple — Unlawful detachment of the Chagos Archipelago and its incorporation into
a new colony, known as the BIOT.
   Process of decolonization of Mauritius not lawfully completed when Mauritius
acceded to independence in 1968.

                                       * *
   Consequences under international law arising from the continued administration
by the United Kingdom of the Chagos Archipelago.
   Decolonization of Mauritius not conducted in a manner consistent with the right
of peoples to self-determination — United Kingdom’s continued administration of
the Chagos Archipelago constitutes a wrongful act entailing the international
responsibility of that State — Continuing character of the unlawful act —
United Kingdom under an obligation to bring an end to its administration of the
Chagos Archipelago as rapidly as possible — Modalities for completing the decol-
onization of Mauritius to be determined by the General Assembly.
   Obligation of all Member States to co-operate with the United Nations to put
the modalities for completing the decolonization of Mauritius into effect — Re-
settlement on the Chagos Archipelago of Mauritian nationals, including those of
Chagossian origin, is an issue relating to the protection of the human rights of
those concerned — Issue should be addressed by the General Assembly during the
completion of the decolonization of Mauritius.

                            ADVISORY OPINION

Present: President Yusuf; Vice-President Xue; Judges Tomka, Abraham,
         Bennouna, Cançado Trindade, Donoghue, Gaja, Sebutinde,
         Bhandari, Robinson, Gevorgian, Salam, Iwasawa; Registrar
         Couvreur.

 On the legal consequences of the separation of the Chagos Archipelago from
Mauritius in 1965,
  The Court,
  composed as above,

                                                                                9

              separation of the chagos (advisory opinion)                    101

  gives the following Advisory Opinion:
   1. The questions on which the advisory opinion of the Court has been
requested are set forth in resolution 71/292 adopted by the General Assembly of
the United Nations (hereinafter the “General Assembly”) on 22 June 2017. By a
letter dated 23 June 2017 and received in the Registry on 28 June 2017, the
Secretary-General of the United Nations oﬃcially communicated to the Court
the decision taken by the General Assembly to submit these questions for an
advisory opinion. Certiﬁed true copies of the English and French texts of the
resolution were enclosed with the letter. The resolution reads as follows:

        “The General Assembly,
        Reaffirming that all peoples have an inalienable right to the exercise of
     their sovereignty and the integrity of their national territory,
        Recalling the Declaration on the Granting of Independence to Colonial
     Countries and Peoples, contained in its resolution 1514 (XV) of 14 Decem-
     ber 1960, and in particular paragraph 6 thereof, which states that any
     attempt aimed at the partial or total disruption of the national unity and
     the territorial integrity of a country is incompatible with the purposes and
     principles of the Charter of the United Nations,
        Recalling also its resolution 2066 (XX) of 16 December 1965, in which it
     invited the Government of the United Kingdom of Great Britain and
     Northern Ireland to take eﬀective measures with a view to the immediate
     and full implementation of resolution 1514 (XV) and to take no action
     which would dismember the Territory of Mauritius and violate its territorial
     integrity, and its resolutions 2232 (XXI) of 20 December 1966 and
     2357 (XXII) of 19 December 1967,
        Bearing in mind its resolution 65/118 of 10 December 2010 on the ﬁftieth
     anniversary of the Declaration on the Granting of Independence to Colonial
     Countries and Peoples, reiterating its view that it is incumbent on the
     United Nations to continue to play an active role in the process of decolo-
     nization, and noting that the process of decolonization is not yet complete,
        Recalling its resolution 65/119 of 10 December 2010, in which it declared
     the period 2011-2020 the Third International Decade for the Eradication of
     Colonialism, and its resolution 71/122 of 6 December 2016, in which it called
     for the immediate and full implementation of the Declaration on the Grant-
     ing of Independence to Colonial Countries and Peoples,

        Noting the resolutions on the Chagos Archipelago adopted by the Organ-
     ization of African Unity and the African Union since 1980, most recently at
     the twenty-eighth ordinary session of the Assembly of the Union, held in
     Addis Ababa on 30 and 31 January 2017, and the resolutions on the Chagos
     Archipelago adopted by the Movement of Non-Aligned Countries since 1983,
     most recently at the Seventeenth Conference of Heads of State or Govern-
     ment of Non-Aligned Countries, held on Margarita Island, Bolivarian
     Republic of Venezuela, from 13 to 18 September 2016, and in particular the
     deep concern expressed therein at the forcible removal by the United King-
     dom of Great Britain and Northern Ireland of all the inhabitants of the Cha-
     gos Archipelago,

                                                                               10

              separation of the chagos (advisory opinion)                     102

        Noting also its decision of 16 September 2016 to include in the agenda of
     its seventy-ﬁrst session the item entitled ‘Request for an advisory opinion
     of the International Court of Justice on the legal consequences of the sep-
     aration of the Chagos Archipelago from Mauritius in 1965’, on the under-
     standing that there would be no consideration of this item before June 2017,
        Decides, in accordance with Article 96 of the Charter of the United
     Nations, to request the International Court of Justice, pursuant to Article 65
     of the Statute of the Court, to render an advisory opinion on the following
     questions:
     (a) ‘Was the process of decolonization of Mauritius lawfully completed
         when Mauritius was granted independence in 1968, following the
         separation of the Chagos Archipelago from Mauritius and having
         regard to international law, including obligations reﬂected in General
         Assembly resolutions 1514 (XV) of 14 December 1960, 2066 (XX) of
         16 December 1965, 2232 (XXI) of 20 December 1966 and 2357 (XXII)
         of 19 December 1967?’;
     (b) ‘What are the consequences under international law, including obliga-
         tions reﬂected in the above-mentioned resolutions, arising from the
         continued administration by the United Kingdom of Great Britain and
         Northern Ireland of the Chagos Archipelago, including with respect to
         the inability of Mauritius to implement a programme for the resettle-
         ment on the Chagos Archipelago of its nationals, in particular those of
         Chagossian origin?’.”
   2. By letters dated 28 June 2017, the Registrar gave notice of the request for
an advisory opinion to all States entitled to appear before the Court, pursuant
to Article 66, paragraph 1, of the Statute.
   3. By an Order dated 14 July 2017, the Court decided, in accordance with
Article 66, paragraph 2, of the Statute, that the United Nations and its Member
States were likely to be able to furnish information on the questions submitted
to it for an advisory opinion, and ﬁxed 30 January 2018 as the time-limit within
which written statements might be submitted to it on those questions and
16 April 2018 as the time-limit within which States and organizations having
presented a written statement might submit written comments on the other writ-
ten statements.

   4. By letters dated 18 July 2017, the Registrar informed the United Nations
and its Member States of the Court’s decisions and transmitted to them a copy
of the Order.
   5. Pursuant to Article 65, paragraph 2, of the Statute, the Secretary-General
of the United Nations, under cover of a letter dated 30 November 2017 from the
United Nations Legal Counsel, communicated to the Court a dossier of docu-
ments likely to throw light upon the questions formulated by the General
Assembly, which was received in the Registry on 4 December 2017.

   6. By a letter dated 10 January 2018 and received in the Registry the same
day, the Legal Counsel of the African Union requested, ﬁrst, that the African
Union be permitted to furnish information, in writing and orally, on the ques-
tions submitted to the Court for an advisory opinion, and, secondly, that it be
granted an extension of one month for the ﬁling of its written statement.

                                                                                11

              separation of the chagos (advisory opinion)                     103

   7. By an Order dated 17 January 2018, the Court decided that the Afri-
can Union was likely to be able to furnish information on the questions submit-
ted to the Court for an advisory opinion and that it might do so within the
time-limits ﬁxed by the Court. By the same Order, the Court further decided to
extend to 1 March 2018 the time-limit within which all written statements might
be presented to the Court, in accordance with Article 66, paragraph 2, of the
Statute, and to extend to 15 May 2018 the time-limit within which States and
organizations having presented a written statement might submit written com-
ments, in accordance with Article 66, paragraph 4, of the Statute.
   8. By letters dated 17 January 2018, the Registrar informed the United Nations
and its Member States, as well as the African Union, of the Court’s decisions
and transmitted to them a copy of the Order.
   9. Within the time-limit thus extended by the Court in its Order of 17 Janu-
ary 2018, written statements were ﬁled in the Registry, in order of their receipt,
by Belize, Germany, Cyprus, Liechtenstein, Netherlands, United Kingdom of
Great Britain and Northern Ireland, Serbia, France, Israel, Russian Federation,
United States of America, Seychelles, Australia, India, Chile, Brazil, Republic
of Korea, Madagascar, China, Djibouti, Mauritius, Nicaragua, the Afri-
can Union, Guatemala, Argentina, Lesotho, Cuba, Viet Nam, South Africa,
Marshall Islands and Namibia.

   10. By a communication dated 5 March 2018, the Registry informed States hav-
ing presented written statements, as well as the African Union, of the list of par-
ticipants having ﬁled written statements in the proceedings and explained that the
Registry had set up a dedicated website from which those statements could be
downloaded. By the same communication, the Registry further informed those
States and the African Union that the Court had decided to hold hearings which
would open on 3 September 2018.
   11. On 14 March 2018, the Court decided, on an exceptional basis, to autho-
rize the late ﬁling of the written statement of the Republic of Niger.
   12. On the same day, the Registrar informed the United Nations, and those
of its Member States which had not presented written statements, that written
statements had been ﬁled in the Registry. By the same communication, the Reg-
istrar also indicated that the Court had decided to hold hearings which would
open on 3 September 2018, during which oral statements and comments might
be presented by the United Nations and its Member States, regardless of whether
or not they had submitted written statements and, as the case may be, written
comments.
   13. On 15 March 2018, the Registrar communicated a full set of the written
statements received in the Registry to all States having submitted written state-
ments, as well as to the African Union.
   14. By communications dated 26 March 2018, the United Nations and its
Member States, as well as the African Union, were asked to inform the Registry,
by 15 June 2018 at the latest, if they intended to take part in the oral proceed-
ings.
   15. Within the time-limit as extended by the Court in its Order of 17 January
2018, written comments were ﬁled in the Registry, in order of their receipt, by the
African Union, Serbia, Nicaragua, United Kingdom of Great Britain and North-
ern Ireland, Mauritius, Seychelles, Guatemala, Cyprus, Marshall Islands,
United States of America and Argentina.
   16. Upon receipt of those written comments, the Registrar, by communica-
tions dated 16 May 2018, informed States having presented written statements,

                                                                                12

              separation of the chagos (advisory opinion)                   104

as well as the African Union, that written comments had been submitted and
that those comments could be downloaded from a dedicated website.

   17. On 22 May 2018, the Registrar transmitted a full set of the written com-
ments to all States having submitted such comments, as well as to the Afri-
can Union.
   18. By letters dated 29 May 2018, the Registrar transmitted to the
United Nations, and to all its Member States that had not participated in the
written proceedings, a full set of the written statements and written comments
ﬁled in the Registry.
   19. By letters dated 21 June 2018, the Registrar communicated to the
United Nations and its Member States, as well as to the African Union, the list
of participants in the oral proceedings and enclosed a detailed schedule of those
proceedings.
   20. By letters dated 26 June 2018, the Registrar informed Member States of
the United Nations participating in the oral proceedings, as well as the Afri-
can Union, of certain practical arrangements regarding the organization of
those proceedings.
   21. By a letter dated 2 July 2018, the Philippines informed the Court that it
would no longer be making a statement during the oral proceedings. By letters
dated 10 July 2018, the Registrar informed Member States of the United Nations
participating in the oral proceedings and the African Union accordingly.

  22. Pursuant to Article 106 of the Rules of Court, the Court decided to make
the written statements and written comments submitted to it accessible to the
public with eﬀect from the opening of the oral proceedings.
  23. In the course of the hearings held from 3 to 6 September 2018, the Court
heard oral statements, in the following order, by:
for the Republic of Mauritius:   H.E. Sir Anerood Jugnauth, GCSK, KCMG,
                                 QC, Minister Mentor, Minister of Defence,
                                 Minister for Rodrigues of the Republic of
                                 Mauritius,
                                 Mr. Pierre Klein, Professor at the Université
                                 libre de Bruxelles,
                                 Ms Alison Macdonald, QC, Barrister at
                                 Matrix Chambers, London,
                                 Mr. Paul S. Reichler, Attorney at Law, Foley
                                 Hoag LLP, member of the Bar of the District
                                 of Columbia,
                                 Mr. Philippe Sands, QC, Professor of Inter-
                                 national Law at University College London,
                                 Barrister at Matrix Chambers, London;

for the United Kingdom           Mr. Robert Buckland, QC, MP, Solicitor
of Great Britain and             General,
Northern Ireland:                Mr. Samuel Wordsworth, QC, member of the
                                 Bar of England and Wales, Essex Court
                                 Chambers,
                                 Ms Philippa Webb, member of the Bar of
                                 England and Wales, 20 Essex Street Cham-
                                 bers,

                                                                              13

                 separation of the chagos (advisory opinion)              105

                                 Sir Michael Wood, KCMG, member of the
                                 Bar of England and Wales, 20 Essex Street
                                 Chambers;
for the Republic of              Ms J. G. S. de Wet, Chief State Law Adviser
South Africa:                    (International Law), Department of Interna-
                                 tional Relations and Co-operation;

for the Federal Republic of      H.E. Mr. Christophe Eick, Ambassador, Legal
Germany:                         Adviser, Federal Foreign Oﬃce, Berlin,

                                 Mr. Andreas Zimmermann, Professor of Inter-
                                 national Law, University of Potsdam;

for the Argentine Republic:      H.E. Mr. Mario Oyarzábal, Ambassador,
                                 Legal Adviser, Ministry of Foreign Aﬀairs and
                                 Worship,
                                 Mr. Marcelo Kohen, Professor of Interna-
                                 tional Law, Graduate Institute of Interna-
                                 tional and Development Studies, Geneva,
                                 Member and Secretary-General of the Institut
                                 de droit international;
for Australia:                   Mr. Bill Campbell, QC,
                                 Mr. Stephen Donaghue, QC, Solicitor General
                                 of Australia;
for Belize:                      Mr. Ben Juratowitch, QC, Attorney at Law,
                                 Belize, and admitted to practice in England
                                 and Wales, and in Queensland, Australia,
                                 Freshﬁelds Bruckhaus Deringer;
for the Republic of Botswana:    Mr. Chuchuchu Nchunga Nchunga, Deputy
                                 Government Attorney, Attorney General’s
                                 Chambers, Botswana,
                                 Mr. Shotaro Hamamoto, Professor of Interna-
                                 tional Law, Kyoto University, Japan;
for the Federative Republic      H.E. Ms Regina Maria Cordeiro Dunlop,
of Brazil:                       Ambassador of the Federative Republic
                                 of Brazil to the Kingdom of the Netherlands;

for the Republic of Cyprus:      H.E. Mr. Costas Clerides, Attorney General
                                 of the Republic of Cyprus,
                                 Ms Mary-Ann Stavrinides, Attorney of the
                                 Republic, Law Oﬃce of the Republic of
                                 Cyprus,
                                 Mr. Polyvios G. Polyviou, Chryssaﬁnis &
                                 Polyviou LLC;
for the United States of         Ms Jennifer G. Newstead, Legal Adviser,
America:                         United States Department of State;
for the Republic                 Mr. Lesther Antonio Ortega Lemus, Minister
of Guatemala:                    Counsellor, Co-Representative of Guatemala,
                                 H.E. Ms Gladys Marithza Ruiz Sánchez
                                 De Vielman, Ambassador, Representative
                                 of Guatemala;

                                                                           14

              separation of the chagos (advisory opinion)                    106

for the Republic of the Marshall Mr. Caleb W. Christopher, Legal Adviser,
Islands:                         Permanent Mission of the Republic of the
                                 Marshall Islands to the United Nations, New
                                 York;
for the Republic of India:       H.E. Mr. Venu Rajamony, Ambassador of
                                 India to the Kingdom of the Netherlands;
for the State of Israel:         Mr. Tal Becker, Legal Adviser, Ministry of
                                 Foreign Aﬀairs,
                                 Mr. Roy Schöndorf, Deputy Attorney Gen-
                                 eral (International Law), Ministry of Justice;
for the Republic of Kenya:       H.E. Mr. Lawrence Lenayapa, Ambassador of
                                 the Republic of Kenya to the Kingdom of the
                                 Netherlands,
                                 Ms Pauline Mcharo, Deputy Chief State
                                 Counsel, Oﬃce of the Attorney General of
                                 Kenya;
for the Republic                 H.E. Mr. Carlos José Argüello Gómez,
of Nicaragua:                    Ambassador of Nicaragua to the Kingdom of
                                 the Netherlands;
for the Federal Republic         Mr. Dayo Apata, Solicitor General of the
of Nigeria:                      Federal Republic of Nigeria, Permanent Sec-
                                 retary, Federal Ministry of Justice;
for the Republic of Serbia:      Mr. Aleksandar Gajić, Chief Legal Counsel at
                                 the Ministry of Foreign Aﬀairs;
for the Kingdom of Thailand:     H.E. Mr. Virachai Plasai, Ambassador of the
                                 Kingdom of Thailand to the United States of
                                 America;
for the Republic of Vanuatu:     Mr. Robert McCorquodale, Brick Court
                                 Chambers, member of the Bar of England and
                                 Wales,
                                 Ms Jennifer Robinson, Doughty Street Cham-
                                 bers, member of the Bar of England and
                                 Wales;
for the Republic of Zambia:      Mr. Likando Kalaluka, SC, Attorney General,
                                 Mr. Dapo Akande, Professor of Public Inter-
                                 national Law, University of Oxford;
for the African Union:           H.E. Ms Namira Negm, Ambassador, Legal
                                 Counsel of the African Union and Director of
                                 Legal Aﬀairs Directorate,
                                 Mr. Mohamed Gomaa, Legal Counsellor and
                                 Arbitrator,
                                 Mr. Makane Moïse Mbengue, Professor of
                                 International Law, University of Geneva, and
                                 Aﬃliate Professor, Institut d’études politiques,
                                 Paris.
  24. At the hearings, a Member of the Court put a question to Mauritius,
which replied in writing, as requested, within the prescribed time-limit. The
Court having decided that the other participants could submit comments or
observations on the reply given by Mauritius, written comments were ﬁled in the
Registry, in order of their receipt, by the African Union, Argentina, United King-
dom of Great Britain and Northern Ireland and United States of America.

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             separation of the chagos (advisory opinion)                  107

Another Member of the Court put a question to all the participants in the oral
proceedings, to which Australia, Botswana and Vanuatu, Nicaragua,
United Kingdom of Great Britain and Northern Ireland, Mauritius, Argentina,
United States of America and Guatemala, in that order, replied in writing, as
requested. The Court having decided that the other participants could submit
comments or observations on the replies thus given, Mauritius, the Afri-
can Union and United States of America submitted such comments or observa-
tions in writing.

                                       *
                                   *       *

          I. Events Leading to the Adoption of the Request
                      for the Advisory Opinion

  25. Before examining the events leading to the adoption of the request
for the advisory opinion, the Court recalls that the Republic of Mauritius
consists of a group of islands in the Indian Ocean comprising approxi-
mately 1,950 sq km. The main island of Mauritius is located about
2,200 km south-west of the Chagos Archipelago, about 900 km east of
Madagascar, about 1,820 km south of Seychelles and about 2,000 km oﬀ
the eastern coast of the African continent.
  26. The Chagos Archipelago consists of a number of islands and atolls.
The largest island is Diego Garcia, located in the south-east of the archi-
pelago. With an area of about 27 sq km, Diego Garcia accounts for more
than half of the archipelago’s total land area.

   27. Although Mauritius was occupied by the Dutch from 1638 to 1710,
the ﬁrst colonial administration of Mauritius was established in 1715 by
France which named it Ile de France. In 1810, the British captured
Ile de France and renamed it Mauritius. By the Treaty of Paris of 1814,
France ceded Mauritius and all its dependencies to the United Kingdom.
   28. Between 1814 and 1965, the Chagos Archipelago was administered
by the United Kingdom as a dependency of the colony of Mauritius.
From as early as 1826, the islands of the Chagos Archipelago were listed
by Governor Lowry-Cole as dependencies of Mauritius. The islands were
also described in several ordinances, including those made by Governors
of Mauritius in 1852 and 1872, as dependencies of Mauritius. The Mau-
ritius Constitution Order of 26 February 1964 (hereinafter the
“1964 Mauritius Constitution Order”), promulgated by the United
Kingdom Government, deﬁned the colony of Mauritius in Section 90 (1)
as “the island of Mauritius and the Dependencies of Mauritius”.
   29. In accordance with General Assembly resolution 66 (I) of
14 December 1946, the United Kingdom as the administering Power reg-
ularly transmitted information to the General Assembly under Arti-
cle 73 (e) of the Charter of the United Nations concerning Mauritius as

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             separation of the chagos (advisory opinion)                  108

a non-self-governing territory. The information submitted by the
United Kingdom was included in several reports of the Fourth Commit-
tee (Special Political and Decolonization Committee) of the General
Assembly. In many of these reports, the islands of the Chagos Archipel-
ago, and sometimes the Chagos Archipelago itself, are referred to as
dependencies of Mauritius. In its 1947 Report, Mauritius is described as
comprising the island of Mauritius and its dependencies among which are
mentioned the island of Rodriguez and the Oil Islands group of which the
principal island is Diego Garcia. The Report of 1948 collectively referred
to all of the islands as “Mauritius”. The Report of 1949 states that “there
are dependent upon Mauritius a number of islands scattered over the
Indian Ocean, of which the most important is Rodriguez . . . Other depen-
dencies are: Chagos Archipelago . . . Agalega and Cargados Charajos”.

   30. On 14 December 1960, the General Assembly adopted resolu-
tion 1514 (XV) entitled “Declaration on the Granting of Independence to
Colonial Countries and Peoples” (hereinafter “resolution 1514 (XV)”).
On 27 November 1961, the General Assembly, by resolution 1654 (XVI),
established the United Nations Special Committee on Decolonization
(hereinafter the “Committee of Twenty-Four”) to monitor the implemen-
tation of resolution 1514 (XV).
   31. In February 1964, discussions commenced between the
United States of America (hereinafter the “United States”) and the
United Kingdom regarding the use by the United States of certain
British-owned islands in the Indian Ocean. The United States expressed
an interest in establishing military facilities on the island of Diego Garcia.
   32. On 29 June 1964, the United Kingdom also commenced talks with
the Premier of the colony of Mauritius regarding the detachment of the
Chagos Archipelago from Mauritius. At Lancaster House, talks between
representatives of the colony of Mauritius and the United Kingdom Gov-
ernment led to the conclusion on 23 September 1965 of an agreement
(hereinafter the “Lancaster House agreement”, described in more detail
in paragraph 108 below).
   33. On 8 November 1965, by the British Indian Ocean Territory
Order 1965, the United Kingdom established a new colony known as the
British Indian Ocean Territory (hereinafter the “BIOT”) consisting of the
Chagos Archipelago, detached from Mauritius, and the Aldabra, Farqu-
har and Desroches Islands, detached from Seychelles.
   34. On 16 December 1965, the General Assembly adopted resolu-
tion 2066 (XX) on the “Question of Mauritius”, in which it expressed
deep concern about the detachment of certain islands from the territory
of Mauritius for the purpose of establishing a military base and invited
the “administering Power to take no action which would dismember the
Territory of Mauritius and violate its territorial integrity”.

   35. On 20 December 1966, the General Assembly adopted resolu-
tion 2232 (XXI) on a number of territories including Mauritius. The reso-
lution reiterated that

                                                                           17

            separation of the chagos (advisory opinion)                   109

    “any attempt aimed at the partial or total disruption of the national
    unity and the territorial integrity of colonial Territories and the estab-
    lishment of military bases and installations in these Territories is
    incompatible with the purposes and principles of the Charter of the
    United Nations and of General Assembly resolution 1514 (XV)”.
   36. The talks between the United Kingdom and the United States
resulted in the conclusion on 30 December 1966 of the “Agreement con-
cerning the Availability for Defence Purposes of the British Indian Ocean
Territory” and the conclusion of an Agreed Minute of the same date.
   37. Based on the 1966 Agreement, the United States and the United
Kingdom agreed that the Government of the United Kingdom would
take any “administrative measures” necessary to ensure that their defence
needs were met. The Agreed Minute provided that, among the adminis-
trative measures to be taken, was “resettling any inhabitants” of the
islands. The inhabitants of the Chagos Archipelago are referred to as
Chagossians and, sometimes, as the “Ilois” or “islanders”. In this Opin-
ion these terms are used interchangeably.
   38. On 10 May 1967, Sub-Committee I of the Committee of
Twenty-Four reported that:
       “By creating a new territory, the British Indian Ocean Territory,
    composed of islands detached from Mauritius and Seychelles, the
    administering Power continues to violate the territorial integrity of
    these Non-Self Governing Territories and to defy resolu-
    tions 2066 (XX) and 2232 (XXI) of the General Assembly.”
   39. On 15, 17 and 19 June 1967, the Committee of Twenty-Four exam-
ined the Report of Sub-Committee I and adopted a resolution on Mauri-
tius. In this resolution, the Committee
    “[d]eplores the dismemberment of Mauritius and Seychelles by the
    administering Power which violates their territorial integrity, in con-
    travention of General Assembly resolutions 2066 (XX) and 2232 (XXI)
    and calls upon the administering Power to return to these Territories
    the islands detached therefrom”.
   40. On 7 August 1967, general elections were held in Mauritius and the
political parties in favour of independence prevailed.
   41. On 19 December 1967, the General Assembly adopted resolu-
tion 2357 (XXII) on a number of territories including Mauritius, and
reaﬃrmed what it had declared in resolution 2232 (XXI) (see para-
graph 35 above).
   42. On 12 March 1968, Mauritius became an independent State and on
26 April 1968 was admitted to membership in the United Nations.
Sir Seewoosagur Ramgoolam became the ﬁrst Prime Minister of the
Republic of Mauritius. Section 111, paragraph 1, of the 1968 Constitu-
tion of Mauritius, promulgated by the United Kingdom Government
before independence on 4 March 1968, deﬁned Mauritius as “the territo-

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            separation of the chagos (advisory opinion)             110

ries which immediately before 12th March 1968 constituted the colony of
Mauritius”. This deﬁnition did not include the Chagos Archipelago in the
territory of Mauritius.
   43. Between 1967 and 1973, the entire population of the Chagos Archi-
pelago was either prevented from returning or forcibly removed and pre-
vented from returning by the United Kingdom. The main forcible removal
of Diego Garcia’s population took place in July and September 1971.

   44. On 11 April 1979, in a discussion on the detachment of the Cha-
gos Archipelago, Prime Minister Ramgoolam told the Mauritian Parlia-
ment “we had no choice”.
   45. In July 1980, the Organization of African Unity (hereinafter the
“OAU”) adopted resolution 99 (XVII) (1980) in which it “demands” that
Diego Garcia be “unconditionally returned to Mauritius”.
   46. On 9 October 1980, the Mauritian Prime Minister, at the thirty-
ﬁfth session of the United Nations General Assembly, stated that the
BIOT should be disbanded and the territory restored to Mauritius as part
of its natural heritage.
   47. In July 2000, the OAU adopted Decision AHG/Dec.159 (XXXVI)
(2000) expressing its concern that the Chagos Archipelago was “excised
by the colonial power from Mauritius prior to its independence in viola-
tion of UN Resolution 1514”.

   48. On 1 April 2010, the United Kingdom announced the creation of a
marine protected area in and around the Chagos Archipelago. On
20 December 2010, Mauritius instituted proceedings against the
United Kingdom pursuant to Article 287 of the United Nations Conven-
tion on the Law of the Sea (hereinafter “UNCLOS” or “the Conven-
tion”) before an Arbitral Tribunal constituted under Annex VII of the
Convention, challenging the creation of a marine protected area by the
United Kingdom. In those proceedings, Mauritius submitted, inter alia,
that (1) the United Kingdom was not entitled to declare a marine pro-
tected area or other maritime zones in and around the Chagos Archipel-
ago as it was not a coastal State within the meaning of UNCLOS; (2) the
United Kingdom was not entitled to declare unilaterally a marine pro-
tected area or other maritime zones because Mauritius had rights as a
coastal State within the meaning of Articles 56, paragraph 1, and 76,
paragraph 8, of UNCLOS; (3) the United Kingdom should not take any
steps to prevent the Commission on the Limits of the Continental Shelf
from making recommendations to Mauritius in respect of any submission
that Mauritius may make to that Commission regarding the Chagos
Archipelago; and (4) the marine protected area was incompatible with the
United Kingdom’s obligations under UNCLOS.

   49. On 27 July 2010, the African Union adopted Decision 331 (2010),
in which it stated that the Chagos Archipelago, including Diego Garcia,
was detached “by the former colonial power from the territory of Mauri-

                                                                     19

             separation of the chagos (advisory opinion)                111

tius in violation of [General Assembly] Resolutions 1514 (XV) of
14 December 1960 and 2066 (XX) of 16 December 1965 which prohibit
colonial powers from dismembering colonial territories prior to granting
independence”.
   50. On 18 March 2015, the Arbitral Tribunal constituted under
Annex VII of UNCLOS rendered an award in the Arbitration regarding
the Chagos Marine Protected Area between Mauritius and the United
Kingdom (hereinafter the “Arbitration regarding the Chagos Marine Pro-
tected Area”). The Tribunal found, in its Award, that it lacked jurisdic-
tion on Mauritius’ ﬁrst, second and third submissions, but had jurisdiction
to consider Mauritius’ fourth submission. With respect to the ﬁrst sub-
mission, the Tribunal observed that “[t]he parties’ dispute regarding sov-
ereignty over the Chagos Archipelago does not concern interpretation or
application” of UNCLOS. On the merits, the Arbitral Tribunal found,
inter alia, that, in establishing the marine protected area surrounding the
Chagos Archipelago, the United Kingdom had breached its obligations
under Article 2, paragraph 3, Article 56, paragraph 2, and Article 194,
paragraph 4, of the Convention, and that the United Kingdom’s under-
taking to return the Chagos Archipelago to Mauritius, when no longer
needed for defence purposes, was legally binding.

   51. On 30 December 2016, the 50-year period covered by the 1966
Agreement came to an end; however, it was extended for a further period
of twenty years, in accordance with its terms.
   52. On 30 January 2017, the Assembly of the African Union adopted
resolution AU/Res.1 (XXVIII) on the Chagos Archipelago which resolved,
among other things, to support Mauritius with a view to ensuring “the
completion of the decolonization of the Republic of Mauritius”.
   53. On 23 June 2017, the General Assembly adopted resolution 71/292
requesting an advisory opinion from the Court (see paragraph 1 above).
Having recalled the events leading to the adoption of that request, the
Court now turns to the consideration of the questions of jurisdiction and
discretion.

                    II. Jurisdiction and Discretion

   54. When the Court is seised of a request for an advisory opinion, it
must ﬁrst consider whether it has jurisdiction to give the opinion requested
and if so, whether there is any reason why the Court should, in the exer-
cise of its discretion, decline to answer the request (see Legality of the
Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports
1996 (I), p. 232, para. 10; Legal Consequences of the Construction of a
Wall in the Occupied Palestinian Territory, Advisory Opinion, I.C.J. Reports
2004 (I), p. 144, para. 13; Accordance with International Law of the Uni-
lateral Declaration of Independence in Respect of Kosovo, Advisory Opin-
ion, I.C.J. Reports 2010 (II), p. 412, para. 17).

                                                                         20

             separation of the chagos (advisory opinion)                  112

                               A. Jurisdiction
   55. The Court’s jurisdiction to give an advisory opinion is based on
Article 65, paragraph 1, of its Statute which provides that “[t]he Court
may give an advisory opinion on any legal question at the request of
whatever body may be authorized by or in accordance with the Charter
of the United Nations to make such a request”.
   56. The Court notes that the General Assembly is competent to request
an advisory opinion by virtue of Article 96, paragraph 1, of the Charter,
which provides that “[t]he General Assembly . . . may request the Inter-
national Court of Justice to give an advisory opinion on any legal ques-
tion”.
   57. The Court now turns to the requirement in Article 96 of the Char-
ter and Article 65 of its Statute that the advisory opinion must be on a
“legal question”.
   58. In the present proceedings, the ﬁrst question put to the Court is
whether the process of decolonization of Mauritius was lawfully com-
pleted having regard to international law when it was granted indepen-
dence following the separation of the Chagos Archipelago. The second
question relates to the consequences arising under international law from
the continued administration by the United Kingdom of the Chagos
Archipelago. The Court considers that a request from the General Assem-
bly for an advisory opinion to examine a situation by reference to inter-
national law concerns a legal question.
   59. The Court therefore concludes that the request has been made in
accordance with the Charter and that the two questions submitted to it
are legal in character.
   60. One of the participants in the present proceedings has argued that
the Court lacks jurisdiction because the questions asked “ostensibly relate
to one topic, but . . . in fact relate to a diﬀerent topic”. Moreover, it con-
tended that there is no “exact statement of the question upon which an
opinion is required” within the meaning of Article 65, paragraph 2, of the
Statute. According to the same participant, the questions put to the Court
do not reﬂect the real issues, which relate to sovereignty rather than
decolonization.
   61. The Court is of the view that the arguments raised in these
proceedings in relation to Article 65, paragraph 2, of its Statute do
not deprive it of jurisdiction to render the advisory opinion. When faced
with similar arguments in its Advisory Opinion on the Legal Conse-
quences of the Construction of a Wall in the Occupied Palestinian Terri-
tory, the Court observed that “lack of clarity in the drafting of a
question does not deprive the Court of jurisdiction. Rather, such
uncertainty will require clariﬁcation in interpretation, and such neces-
sary clariﬁcations of interpretation have frequently been given by the
Court.” (Advisory Opinion, I.C.J. Reports 2004 (I), pp. 153-154, para. 38.)
The Court will examine these arguments in paragraphs 135
to 137 below.

                                                                           21

             separation of the chagos (advisory opinion)                  113

  62. The Court accordingly has jurisdiction to give the advisory opinion
requested by resolution 71/292 of the General Assembly.

                               B. Discretion
  63. The fact that the Court has jurisdiction does not mean, however,
that it is obliged to exercise it:
       “The Court has recalled many times in the past that Article 65,
    paragraph 1, of its Statute, which provides that ‘The Court may give
    an advisory opinion . . .’, should be interpreted to mean that the Court
    has a discretionary power to decline to give an advisory opinion even
    if the conditions of jurisdiction are met.” (Legal Consequences of the
    Construction of a Wall in the Occupied Palestinian Territory, Advisory
    Opinion, I.C.J. Reports 2004 (I), p. 156, para. 44; Accordance with
    International Law of the Unilateral Declaration of Independence in
    Respect of Kosovo, Advisory Opinion, I.C.J. Reports 2010 (II),
    pp. 415-416, para. 29.)

   64. The discretion whether or not to respond to a request for an advi-
sory opinion exists so as to protect the integrity of the Court’s judicial
function as the principal judicial organ of the United Nations (Legal Con-
sequences of the Construction of a Wall in the Occupied Palestinian Terri-
tory, Advisory Opinion, I.C.J. Reports 2004 (I), pp. 156-157, paras. 44-45;
Accordance with International Law of the Unilateral Declaration of Inde-
pendence in Respect of Kosovo, Advisory Opinion, I.C.J. Reports 2010 (II),
pp. 415-416, para. 29).
   65. The Court is, nevertheless, mindful of the fact that its answer to a
request for an advisory opinion “represents its participation in the activi-
ties of the Organization, and, in principle, should not be refused” (Inter-
pretation of Peace Treaties with Bulgaria, Hungary and Romania, First
Phase, Advisory Opinion, I.C.J. Reports 1950, p. 71; Difference Relating to
Immunity from Legal Process of a Special Rapporteur of the Commission
on Human Rights, Advisory Opinion, I.C.J. Reports 1999 (I), pp. 78-79,
para. 29; Legal Consequences of the Construction of a Wall in the Occupied
Palestinian Territory, Advisory Opinion, I.C.J. Reports 2004 (I), p. 156,
para. 44). Thus, the consistent jurisprudence of the Court is that only
“compelling reasons” may lead the Court to refuse its opinion in response
to a request falling within its jurisdiction (Legal Consequences of the Con-
struction of a Wall in the Occupied Palestinian Territory, Advisory Opin-
ion, I.C.J. Reports 2004 (I), p. 156, para. 44; Accordance with International
Law of the Unilateral Declaration of Independence in Respect of Kosovo,
Advisory Opinion, I.C.J. Reports 2010 (II), p. 416, para. 30).
   66. The Court must satisfy itself as to the propriety of the exercise of
its judicial function in the present proceedings. It will therefore give care-
ful consideration as to whether there are compelling reasons for it to
decline to respond to the request from the General Assembly.

                                                                           22

             separation of the chagos (advisory opinion)                  114

  67. Some participants in the present proceedings have argued that
there are “compelling reasons” for the Court to exercise its discretion to
decline to give the advisory opinion requested. Among the reasons raised
by these participants are that, ﬁrst, advisory proceedings are not suitable
for determination of complex and disputed factual issues; secondly,
the Court’s response would not assist the General Assembly in the perfor-
mance of its functions; thirdly, it would be inappropriate for the Court
to re-examine a question already settled by the Arbitral Tribunal consti-
tuted under Annex VII of UNCLOS in the Arbitration regarding the Cha-
gos Marine Protected Area; and fourthly, the questions asked in the
present proceedings relate to a pending bilateral dispute between two
States which have not consented to the settlement of that dispute by the
Court.
  68. The Court will now turn to the examination of these arguments.

1. Whether advisory proceedings are suitable for determination of complex
   and disputed factual issues
   69. It has been argued by some participants that the questions raise
complex and disputed factual issues which are not suitable for determina-
tion in advisory proceedings. Those participants have contended that in
these proceedings the Court does not have suﬃcient information and evi-
dence to arrive at a conclusion on the complex and disputed questions of
fact before it.
   70. Other participants have maintained that the factual issues before
the Court are not complex and that what really matters is the Court’s
interpretation of those facts.
   71. The Court recalls that in its Advisory Opinion on Western Sahara
when it was faced with the same argument, it concluded that what was
decisive was whether it had
    “suﬃcient information and evidence to enable it to arrive at a judicial
    conclusion upon any disputed questions of fact the determination of
    which is necessary for it to give an opinion in conditions compatible
    with its judicial character” (I.C.J. Reports 1975, pp. 28-29, para. 46).
   72. Moreover, the Court recalls that, in its Advisory Opinion on Legal
Consequences for States of the Continued Presence of South Africa in
Namibia (South West Africa) notwithstanding Security Council Resolu-
tion 276 (1970), it held that
    “to enable [it] to pronounce on legal questions, it must also be
    acquainted with, take into account and, if necessary, make ﬁndings
    as to the relevant factual issues” (I.C.J. Reports 1971, p. 27, para. 40).

  73. The Court observes that an abundance of material has been pre-
sented before it including a voluminous dossier from the United Nations.
Moreover, many participants have submitted written statements and

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             separation of the chagos (advisory opinion)               115

written comments and made oral statements which contain information
relevant to answering the questions. Thirty-one States and the Afri-
can Union ﬁled written statements, ten of those States and the African
Union submitted written comments thereon, and twenty-two States and
the African Union made oral statements. The Court notes that informa-
tion provided by participants includes the various oﬃcial records from
the 1960s, such as those from the United Kingdom concerning the detach-
ment of the Chagos Archipelago and the accession of Mauritius to inde-
pendence.

  74. The Court is therefore satisﬁed that there is in the present proceed-
ings suﬃcient information on the facts before it for the Court to give the
requested opinion. Accordingly, the Court cannot decline to answer the
questions put to it.

2. Whether the Court’s response would assist the General Assembly in the
   performance of its functions

   75. It has been argued by some participants that the advisory opinion
requested would not assist the General Assembly in the proper exercise of
its functions. These participants have maintained that the General Assem-
bly has not been actively engaged in the decolonization of Mauritius since
1968. In particular, they have asserted that, after Mauritius became inde-
pendent in March 1968, it was removed from the list of territories being
monitored by the Committee of Twenty-Four and that the Chagos Archi-
pelago was never added to that list. Other participants have argued that
the Court’s response would be useful to the General Assembly, which
continued to be active after 1968 in considering the question of Mauritius
and the detachment of the Chagos Archipelago.
   76. The Court considers that it is not for the Court itself to determine
the usefulness of its response to the requesting organ. Rather, it should
be left to the requesting organ, the General Assembly, to determine
“whether it needs the opinion for the proper performance of its func-
tions” (Accordance with International Law of the Unilateral Declaration of
Independence in Respect of Kosovo, Advisory Opinion, I.C.J. Reports
2010 (II), p. 417, para. 34). The Court recalls that, in its Advisory Opin-
ion on Legality of the Threat or Use of Nuclear Weapons, it did not accept
an argument that the Court should refuse to respond to the General
Assembly’s request on the ground that the General Assembly had not
explained to the Court the purposes for which it sought an opinion. The
Court observed that:
    “it is not for the Court itself to purport to decide whether or not an
    advisory opinion is needed by the Assembly for the performance of
    its functions. The General Assembly has the right to decide for itself
    on the usefulness of an opinion in the light of its own needs.”
    (I.C.J. Reports 1996 (I), p. 237, para. 16.)

                                                                        24

             separation of the chagos (advisory opinion)                   116

   77. In the Advisory Opinion on Legal Consequences of the Construc-
tion of a Wall in the Occupied Palestinian Territory, the Court stated that
it “cannot substitute its assessment of the usefulness of the opinion
requested for that of the organ that seeks such opinion” (I.C.J. Reports
2004 (I), p. 163, para. 62). The Court recalls that “[i]n any event, to what
extent or degree its opinion will have an impact on the action of the Gen-
eral Assembly is not for the Court to decide” (Western Sahara, Advisory
Opinion, I.C.J. Reports 1975, p. 37, para. 73).
   78. It follows that in the present proceedings the Court cannot decline
to answer the questions posed to it by the General Assembly in resolu-
tion 71/292 on the ground that its opinion would not assist the General
Assembly in the performance of its functions.

3. Whether it would be appropriate for the Court to re-examine a question
   allegedly settled by the Arbitral Tribunal constituted under UNCLOS
   Annex VII in the Arbitration regarding the Chagos Marine Protected
   Area
   79. Certain participants have argued that an advisory opinion by the
Court would reopen the ﬁndings of the Arbitral Tribunal in the Arbitra-
tion regarding the Chagos Marine Protected Area that are binding on
Mauritius and the United Kingdom.
   80. Other participants have contended that res judicata does not apply
in these proceedings because the same parties are not seeking to litigate
the same issue that has already been deﬁnitively settled between them in
an earlier case.

   81. The Court recalls that its opinion “is given not to States, but to the
organ which is entitled to request it” (Interpretation of Peace Treaties with
Bulgaria, Hungary and Romania, First Phase, Advisory Opinion,
I.C.J. Reports 1950, p. 71). The Court observes that the principle of res judi-
cata does not preclude it from rendering an advisory opinion. When
answering a question submitted for an opinion, the Court will consider any
relevant judicial or arbitral decision. In any event, the Court further notes
that the issues that were determined by the Arbitral Tribunal in the Arbitra-
tion regarding the Chagos Marine Protected Area (see paragraph 50 above)
are not the same as those that are before the Court in these proceedings.
   82. It follows from the foregoing that the Court cannot decline to
answer the questions on this ground.

4. Whether the questions asked relate to a pending dispute between two
   States, which have not consented to its settlement by the Court
  83. Some participants have argued that there is a bilateral dispute
between Mauritius and the United Kingdom regarding sovereignty over
the Chagos Archipelago and that this dispute is at the core of the advisory
proceedings. According to those participants, to determine the issues in

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             separation of the chagos (advisory opinion)                 117

the present proceedings, the Court would be required to arrive at conclu-
sions on certain key points such as the eﬀect of the 1965 Lancaster House
agreement. Certain participants have contended that the dispute over sov-
ereignty, which arose in the 1980s in bilateral relations, is the “real dis-
pute” that motivates the request. These participants have further contended
that Mauritius’ claims in the Arbitration regarding the Chagos Marine Pro-
tected Area revealed the existence of a bilateral territorial dispute between
that State and the United Kingdom. Therefore, to render an advisory
opinion would contravene “the principle that a State is not obliged to
allow its disputes to be submitted to judicial settlement without its con-
sent” (Western Sahara, Advisory Opinion, I.C.J. Reports 1975, pp. 24-25,
paras. 32-33; Interpretation of Peace Treaties with Bulgaria, Hungary and
Romania, First Phase, Advisory Opinion, I.C.J. Reports 1950, p. 71).
   84. Other participants have maintained that there is no territorial dis-
pute between the United Kingdom and Mauritius that would prevent the
Court from giving the advisory opinion requested. In particular, they
have argued that the questions put to the Court by the General Assembly
concern issues located in a broader frame of reference, that is, the law of
decolonization and the exercise of the right to self-determination. Some
participants have argued that the dispute between Mauritius and the
United Kingdom relating to territorial sovereignty over the Chagos
Archipelago could neither have arisen independently nor could it be
detached from the question of decolonization. Other participants have
contended that the United Kingdom, having undertaken in 1965 to return
the Chagos Archipelago to Mauritius once it was no longer needed for
defence purposes, recognized that the archipelago belonged to Mauritius,
and accordingly there could be no territorial dispute.
   85. The Court recalls that there would be a compelling reason for it to
decline to give an advisory opinion when such a reply “would have the
eﬀect of circumventing the principle that a State is not obliged to allow its
disputes to be submitted to judicial settlement without its consent” (West-
ern Sahara, Advisory Opinion, I.C.J. Reports 1975, p. 25, para. 33).
   86. The Court notes that the questions put to it by the General Assem-
bly relate to the decolonization of Mauritius. The General Assembly has
not sought the Court’s opinion to resolve a territorial dispute between
two States. Rather, the purpose of the request is for the General Assem-
bly to receive the Court’s assistance so that it may be guided in the dis-
charge of its functions relating to the decolonization of Mauritius. The
Court has emphasized that it may be in the interest of the General Assem-
bly to seek an advisory opinion which it deems of assistance in carrying
out its functions in regard to decolonization:
      “The object of the General Assembly has not been to bring before
    the Court, by way of a request for advisory opinion, a dispute or legal
    controversy, in order that it may later, on the basis of the Court’s
    opinion, exercise its powers and functions for the peaceful settlement
    of that dispute or controversy. The object of the request is an entirely

                                                                          26

             separation of the chagos (advisory opinion)                  118

    diﬀerent one: to obtain from the Court an opinion which the Gen-
    eral Assembly deems of assistance to it for the proper exercise of its
    functions concerning the decolonization of the territory.” (Western
    Sahara, Advisory Opinion, I.C.J Reports 1975, pp. 26-27, para. 39.)
   87. The Court observes that the General Assembly has a long and con-
sistent record in seeking to bring colonialism to an end. From the earliest
days of the United Nations, the General Assembly has played an active
role in matters of decolonization. Article 1, paragraph 2, of the Charter
establishes, as one of the purposes of the United Nations, respect for the
principle of equal rights and self-determination of peoples. In this regard,
the Court notes that Chapter XI of the Charter of the United Nations
relates to non-self-governing territories and that the ﬁrst article in that
Chapter, Article 73, provides that administering powers of non-
self-governing territories are required, inter alia, to “transmit regularly to
the Secretary-General for information purposes . . . statistical and other
information of a technical nature relating to economic, social, and educa-
tional conditions in the territories for which they are respectively respon-
sible”. This information was considered by the Fourth Committee (Special
Political and Decolonization Committee) of the General Assembly and
included in its reports. The work of the Committee continued until 1961
when the Committee of Twenty-Four was established.
   88. The Court therefore concludes that the opinion has been requested
on the matter of decolonization which is of particular concern to the
United Nations. The issues raised by the request are located in the broader
frame of reference of decolonization, including the General Assembly’s
role therein, from which those issues are inseparable (Western Sahara,
Advisory Opinion, I.C.J. Reports 1975, p. 26, para. 38; Legal Consequences
of the Construction of a Wall in the Occupied Palestinian Territory, Advi-
sory Opinion, I.C.J. Reports 2004 (I), p. 159, para. 50).
   89. Moreover, the Court observes that there may be diﬀerences of
views on legal questions in advisory proceedings (Legal Consequences for
States of the Continued Presence of South Africa in Namibia (South West
Africa) notwithstanding Security Council Resolution 276 (1970), Advisory
Opinion, I.C.J. Reports 1971, p. 24, para. 34). However, the fact that the
Court may have to pronounce on legal issues on which divergent views
have been expressed by Mauritius and the United Kingdom does not
mean that, by replying to the request, the Court is dealing with a bilateral
dispute.
   90. In these circumstances, the Court does not consider that to give the
opinion requested would have the eﬀect of circumventing the principle of
consent by a State to the judicial settlement of its dispute with another
State. The Court therefore cannot, in the exercise of its discretion, decline
to give the opinion on that ground.
   91. In light of the foregoing, the Court concludes that there are no
compelling reasons for it to decline to give the opinion requested by the
General Assembly.

                                                                           27

             separation of the chagos (advisory opinion)               119

    III. The Factual Context of the Separation of the Chagos
                  Archipelago from Mauritius

   92. The Court notes that the questions submitted to it by the General
Assembly relate to the separation of the Chagos Archipelago from Mau-
ritius and the legal consequences arising from the continued administra-
tion by the United Kingdom of the Chagos Archipelago (see paragraph 1
above). Before addressing these questions, the Court deems it important
to examine the factual circumstances surrounding the separation of the
archipelago from Mauritius, as well as those relating to the removal of
the Chagossians from this territory.
   93. In this regard, the Court notes that, prior to the separation of the
Chagos Archipelago from Mauritius, there were formal discussions between
the United Kingdom and the United States and between the Government
of the United Kingdom and the representatives of the colony of Mauritius.

 A. The Discussions between the United Kingdom and the United States
                with respect to the Chagos Archipelago
   94. In February 1964, talks commenced between the Governments of
the United Kingdom and the United States on the “strategic use of cer-
tain small British-owned islands in the Indian Ocean” for defence pur-
poses. During these talks, the United States expressed an interest
in establishing a military communication facility on Diego Garcia. At
the end of the talks, it was agreed that the United Kingdom delegation
would recommend to its Government that it should be responsible for
acquiring land, resettling the population and providing compensation
at the United Kingdom Government’s expense; that the Govern-
ment of the United States would be responsible for construction and
maintenance costs and that the United Kingdom Government would
assess quickly the feasibility of the transfer of the administration of
Diego Garcia and the other islands of the Chagos Archipelago from
Mauritius.
   95. According to a memorandum of the United Kingdom Foreign
Oﬃce, the United Kingdom was of the view that the course of action that
would best satisfy its major interests would appear to be to detach
Diego Garcia and other islands in the Chagos Archipelago from Mauri-
tius prior to the latter’s independence, and to place these islands under
the direct administration of the United Kingdom, and that this action
could be done by Order in Council. The United Kingdom considered that
it had the constitutional power to take such action without the consent of
Mauritius, but that such an approach would expose it to criticism in the
United Nations. The same document also indicated that such criticism
would lose most of its force if prior acceptance by the Mauritian Minis-
ters of the detachment was obtained by the United Kingdom, whether
such acceptance was obtained by positive consent or by acquiescence.
The document further stated that it would best suit the interests of the

                                                                        28

              separation of the chagos (advisory opinion)                   120

United Kingdom if the detachment of the Chagos Archipelago was pre-
sented to Mauritius as “a fait accompli” or at most if Mauritius was told
of the United Kingdom’s plans “at the last moment”.
   96. According to a declassiﬁed internal United Kingdom document dated
23 and 24 September 1965 (Record of UK-US Talks on Defence Facilities
in the Indian Ocean, United Kingdom, FO 371/184529), the Governments
of the United Kingdom and the United States considered that, rather than
detaching the islands of the Chagos Archipelago from Mauritius and the
islands of Aldabra, Farquhar and Desroches from Seychelles in two sepa-
rate operations, their interests would be better served by carrying out the
detachment “as a single operation” in order to avoid “a second row” in
the United Nations. According to the same document, during the talks, the
United Kingdom explained to the United States that the detachment of the
Chagos Archipelago from Mauritius would take place in three stages; in
the ﬁnal stage it was envisaged that, when the defence facilities were installed
on an island, “it would be free from local civilian inhabitants”.

   97. The discussions between the United Kingdom and the United States
led to the conclusion of the 1966 Agreement for the establishment of a
military base by the United States on the Chagos Archipelago (see para-
graph 36 above).

   B. The Discussions between the Government of the United Kingdom
          and the Representatives of the Colony of Mauritius
                with respect to the Chagos Archipelago
   98. The 1964 Mauritius Constitution Order, promulgated by the
United Kingdom Government, established a Legislative Assembly con-
sisting of 40 elected members, the Speaker and the Chief Secretary ex offi-
cio and up to 15 members nominated by the Governor. The nominated
members of the Legislative Assembly held oﬃce at the pleasure of
the Governor. There was established a Council of Ministers for
Mauritius consisting of 10 to 13 appointed members, the Chief
Secretary of Mauritius and the Premier of Mauritius; and temp-
orary members who could replace an appointed member who was ill or
absent from the island of Mauritius. The members of the Council were
appointed by the Governor, after consultation with the Premier. They
had to be members of the Legislative Assembly. In the discussions
between the Government of the United Kingdom and the representatives
of the colony of Mauritius, the latter was represented by the Premier of
Mauritius, or by the Premier and other members of the Council of
Ministers.
   99. In 1964, the Committee of Twenty-Four reported that the Consti-
tution of Mauritius did not allow the representatives of the people to
exercise real powers, and that authority was virtually all concentrated in
the hands of the United Kingdom Government (see paragraph 172
below).

                                                                             29

             separation of the chagos (advisory opinion)               121

   100. On 29 June 1964, Mr. John Rennie, the Governor of Mauritius,
discussed with Sir Seewoosagur Ramgoolam, the Premier of Mauritius,
the idea of detaching the Chagos Archipelago from Mauritius. Although
he was favourably disposed to providing “facilities”, the Premier indi-
cated that he preferred a long-term lease rather than detachment.
   101. On 19 July 1965, the Governor of Mauritius was instructed by the
Colonial Oﬃce to inform the Mauritian Council of Ministers of the pro-
posal to detach the Chagos Archipelago by constitutionally separating it
from Mauritius. On 30 July 1965, the Governor of Mauritius informed
the Colonial Oﬃce that the Council of Ministers opposed the detachment
because of the negative public reaction that it would receive in Mauritius.
The Governor indicated that the Council of Ministers expressed a prefer-
ence for a long-term lease of the islands, while the United Kingdom indi-
cated that a lease was not acceptable.

   102. On 3 September 1965, Sir Seewoosagur Ramgoolam and
Sir Anthony Greenwood, the United Kingdom’s Secretary of State for
the Colonies, met in London prior to the start of the Fourth Constitu-
tional Conference and agreed that the discussion on the detachment and
the constitutional conference should be kept separate. However, it appears
that this approach was later modiﬁed to link both matters in a possible
package deal.
   103. On 7 September 1965, the Fourth Constitutional Conference
commenced in London and ended on 24 September 1965. Previous con-
stitutional conferences were held in July 1955, February 1957 and
June 1961. During the Fourth Constitutional Conference, there were sev-
eral private meetings on defence matters. The ﬁrst meeting on 13 Septem-
ber 1965 was attended by Sir Seewoosagur Ramgoolam, Sir Anthony
Greenwood, and Mr. John Rennie. At the meeting, the Premier stated
that Mauritius preferred a lease rather than a detachment of the Cha-
gos Archipelago. Following the meeting, the United Kingdom Foreign
Secretary and the Defence Secretary concluded that if Mauritius would
not agree to the detachment, they would have to “adopt the Foreign Oﬃce
and Ministry of Defence recommendation of ‘forcible detachment and
compensation paid into a fund’”.

   104. On 20 September 1965, during a meeting on defence matters
chaired by the United Kingdom Secretary of State, the Premier of Mau-
ritius again stated that “the Mauritius Government was not interested in
the excision of the islands and would stand out for a 99-year lease”. As an
alternative, the Premier of Mauritius proposed that the United Kingdom
ﬁrst concede independence to Mauritius and thereafter allow the Mauri-
tian Government to negotiate with the Governments of the United King-
dom and the United States on the question of Diego Garcia. During
those discussions, the Secretary of State indicated that a lease would not
be acceptable to the United States and that the Chagos Archipelago
would have to be made available on the basis of its detachment.

                                                                        30

            separation of the chagos (advisory opinion)               122

  105. On 22 September 1965, a Note was prepared by Sir Oliver Wright,
Private Secretary to the United Kingdom’s Prime Minister, Sir Harold
Wilson. It read:
      “Sir Seewoosagur Ramgoolam is coming to see you at 10:00 tomor-
    row morning. The object is to frighten him with hope: hope that he
    might get independence; Fright lest he might not unless he is sensible
    about the detachment of the Chagos Archipelago. I attach a brief
    prepared by the Colonial Oﬃce, with which the Ministry of Defence
    and the Foreign Oﬃce are on the whole content. The key sentence in
    the brief is the last sentence of it on page three.”

  106. The key last sentence referred to above read:
       “The Prime Minister may therefore wish to make some oblique
    reference to the fact that H.M.G. have the legal right to detach Cha-
    gos by Order in Council, without Mauritius consent but this would be
    a grave step.” (Emphasis in the original.)

  107. On 23 September 1965 two events took place. The ﬁrst event was
a meeting in the morning of 23 September 1965 between Prime Minister
Wilson and Premier Ramgoolam. Sir Oliver Wright’s Report on the
meeting indicated that Prime Minister Wilson told Premier Ramgoolam
that
    “in theory there were a number of possibilities. The Premier and his
    colleagues could return to Mauritius either with Independence or
    without it. On the defence point, Diego Garcia could either be
    detached by order in Council or with the agreement of the Premier
    and his colleagues. The best solution of all might be Independence
    and detachment by agreement, although he could not of course com-
    mit the Colonial Secretary at this point.”
   108. The second event on the same day was a meeting on defence mat-
ters held at Lancaster House between Premier Ramgoolam, three other
Mauritian Ministers and the United Kingdom Secretary of State. At the
end of that meeting, the United Kingdom Secretary of State enquired
whether the Mauritian Ministers could agree to the detachment of the
Chagos Archipelago on the basis of undertakings that he would recom-
mend to the Cabinet. The undertakings in the Lancaster House agree-
ment, contained in paragraph 22 of the Record of the Meeting of
23 September 1965, were:
    “(i) negotiations for a defence agreement between Britain and Mau-
         ritius;
    (ii) in the event of independence an understanding between the two
         governments that they would consult together in the event of a
         diﬃcult internal security situation arising in Mauritius;

                                                                       31

              separation of the chagos (advisory opinion)                   123

      (iii) compensation totalling up to £3[million] should be paid to the
            Mauritius Government over and above direct compensation to
            landowners and the cost of resettling others aﬀected in the Cha-
            gos Islands;

      (iv) the British Government would use their good oﬃces with the
           United States Government in support of Mauritius’ request for
           concessions over sugar imports and the supply of wheat and other
           commodities;
       (v) that the British Government would do their best to persuade the
           American Government to use labour and materials from Mauri-
           tius for construction work in the islands;

      . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     (vii) that if the need for the facilities on the islands disappeared the
           islands should be returned to Mauritius”.
The Premier of Mauritius informed the Secretary of State for the Colo-
nies that the proposals put forward by the United Kingdom were accept-
able in principle, but that he would discuss the matter with his other
ministerial colleagues.
  109. On 24 September 1965, the Government of the United Kingdom
announced that it was in favour of granting independence to
Mauritius.
  110. On 6 October 1965, the Secretary of State for the Colonies com-
municated to the Governor of Mauritius the United Kingdom’s accep-
tance of the following additional understanding that had been sought by
the Premier of Mauritius:
(i)  The British Government would use their good oﬃces with the
     United States Government to ensure that the following facilities in
     the Chagos Archipelago would remain available to the Mauritius
     Government as far as practicable:
     (a) navigational and meteorological facilities;
     (b) ﬁshing rights;
     (c) use of air strip for emergency landing and for refuelling civil
         planes without disembarkation of passengers.
(ii) That the beneﬁt of any minerals or oil discovered in or near the Cha-
     gos Archipelago should revert to the Mauritius Government.
This additional understanding was eventually incorporated into the ﬁnal
record of the meeting at Lancaster House and formed part of the Lan-
caster House agreement.
  111. In a Minute sent on 5 November 1965 to the United Kingdom
Prime Minister, the Secretary of State for the Colonies expressed concern
that the United Kingdom would be accused of “creating a . . .
colony in a period of decolonization and of establishing new military
bases when we should be getting out of the old ones”. The Foreign Oﬃce

                                                                              32

             separation of the chagos (advisory opinion)              124

also advised that “the islands chosen have virtually no permanent
inhabitants”.
   112. On 5 November 1965, the Governor of Mauritius informed the
United Kingdom Secretary of State that the Mauritius Council of
Ministers “conﬁrmed agreement to the detachment of the Chagos Archi-
pelago”. The Governor noted that agreement had been given on the
conditions set out in paragraph 22 of the Record of the Meeting of
23 September 1965 (which contained the Lancaster House agreement)
and that the Council of Ministers had formulated an additional under-
standing.

                  C. The Situation of the Chagossians
   113. In the early nineteenth century, several hundred persons were
brought to the Chagos Archipelago from Mozambique and Madagascar
and enslaved to work on coconut plantations owned by British nationals
who lived on the island of Mauritius. In the 1830s, 60,000 enslaved per-
sons in Mauritius, including those in the Chagos Archipelago, were set
free.
   114. Following the 1966 Agreement (see paragraph 36 above), between
1967 and 1973, the inhabitants of the Chagos Archipelago who had left
the islands were prevented from returning. The other inhabitants were
forcibly removed and prevented from returning to the islands (see para-
graph 43 above).
   115. On 16 April 1971, the BIOT Commissioner enacted the Immigra-
tion Ordinance 1971, which made it unlawful for any person to enter or
remain in the Chagos Archipelago without a permit. It also provided for
the Commissioner to make an order directing the removal of such a per-
son from the Chagos Archipelago (Chagos Islanders v. Attorney General
and BIOT Commissioner (2003), EWHC 2222, para. 34).
   116. In the oral proceedings, the United Kingdom reiterated that it
“fully accepts that the manner in which the Chagossians were removed
from the Chagos Archipelago, and the way they were treated thereafter,
was shameful and wrong, and it deeply regrets that fact”.
   117. On 4 September 1972, by virtue of an agreement concluded
between Mauritius and the United Kingdom, Mauritius accepted pay-
ment of the sum of £650,000 in full and ﬁnal discharge of the United King-
dom’s undertaking given in 1965 to meet the cost of resettlement of
persons displaced from the Chagos Archipelago. On 24 March 1973,
Prime Minister Ramgoolam wrote to the British High Commissioner
in Port Louis, acknowledging receipt of the sum of £650,000, but empha-
sizing that the payment did not aﬀect the verbal agreement on minerals,
ﬁshing and prospecting rights reached at Lancaster House on 23 Septem-
ber 1965 and was subject to the remaining Lancaster House undertakings,
including the return of the islands to Mauritius without compensation
if the need for use by the United Kingdom of the islands no longer
existed.

                                                                       33

             separation of the chagos (advisory opinion)                125

  118. In February 1975, Mr. Michel Vencatessen, a former resident of
the Chagos Archipelago, brought an action against the United Kingdom
Government claiming damages for intimidation, deprivation of liberty
and assault in relation to his removal from the Chagos Archipelago in
1971. In 1982, the claim was stayed by agreement of the parties.

   119. On 7 July 1982, an agreement was concluded between the Gov-
ernments of Mauritius and the United Kingdom, for the payment by the
United Kingdom of the sum of £4 million on an ex gratia basis, with no
admission of liability on the part of the United Kingdom, “in full and
ﬁnal settlement of all claims whatsoever of the kind referred to in Arti-
cle 2 of this Agreement against . . . the United Kingdom by or on behalf
of the Ilois”. According to Recital 2 of the preamble to the Agreement,
the term “Ilois” has to be understood as those who went to Mauritius on
their departure or removal from the Chagos Archipelago after Novem-
ber 1965. Article 2 provides:

       “The claims referred to in Article 1 of this Agreement are solely
    claims by or on behalf of the Ilois arising out of:

    (a) All acts, matters and things done by or pursuant to the British
        Indian Ocean Territory Order 1965, including the closure of the
        plantations in the Chagos Archipelago, the departure or removal
        of those living or working there, the termination of their con-
        tracts, their transfer to and resettlement in Mauritius and their
        preclusion from returning to the Chagos Archipelago (hereinafter
        referred to as ‘the events’); and
    (b) Any incidents, facts or situations, whether past, present or future,
        occurring in the course of the events or arising out of the conse-
        quences of the events.”
Article 4 requires Mauritius “to procure from each member of the Ilois
community in Mauritius a signed renunciation of the claims”.
   120. The sum of approximately £4 million paid by the United King-
dom was disbursed to 1,344 islanders between 1983 and 1984. As a condi-
tion for collecting the funds, the islanders were required to sign or to
place a thumbprint on a form renouncing the right to return to the Cha-
gos Archipelago. The form was a one-page legal document, written in
English, without a Creole translation. Only 12 persons refused to sign
(Chagos Islanders v. Attorney General and BIOT Commissioner (2003),
EWHC 2222, para. 80).

   121. In 1998, Mr. Louis Olivier Bancoult, a Chagossian, instituted pro-
ceedings in the United Kingdom courts challenging the validity of legisla-
tion denying him the right to reside in the Chagos Archipelago. On

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             separation of the chagos (advisory opinion)                  126

3 November 2000, judgment was given in his favour by the Divisional
Court which ruled that the relevant provisions of the 1971 Ordinance be
quashed (Regina (Bancoult) v. Secretary of State for Foreign and Common-
wealth Affairs and Another (No. 1) (2000)). The United Kingdom Govern-
ment did not appeal the ruling and it repealed the 1971 Ordinance that had
prohibited Chagossians from returning to the Chagos Archipelago. The
United Kingdom’s Foreign Secretary announced that the United Kingdom
Government was examining the feasibility of resettling the Ilois.
   122. On the same day that the Divisional Court rendered the judgment
in Mr. Bancoult’s favour, the United Kingdom made another immigra-
tion ordinance applicable to the Chagos Archipelago, with the exception
of Diego Garcia (Ordinance No. 4 of 2000). The ordinance provided that
restrictions on entry into and residence in the archipelago would not
apply to the Chagossians, given their connection to the Chagos Islands.
In its written statement, the United Kingdom has submitted that, follow-
ing the adoption of that ordinance, none of the Chagossians returned to
live there although there was no legal bar to them doing so. Chagossians
were however not permitted to enter or reside in Diego Garcia.
   123. On 6 December 2001, the Human Rights Committee, constituted
under the International Covenant on Civil and Political Rights, in consid-
ering the periodic reports submitted by the United Kingdom under Arti-
cle 40 of the said Covenant, noted “the State party’s acceptance that its
prohibition of the return of Ilois who had left or been removed from the
territory was unlawful”. It recommended that “the State party should, to
the extent still possible, seek to make exercise of the Ilois’ right to return
to their territory practicable”.
   124. In June 2002, a feasibility study commissioned by the BIOT
Administration concerning the Chagos Archipelago was completed. It
was carried out in response to a request made by former inhabitants of
the Chagos Archipelago to be permitted to return and live in the archi-
pelago. The study indicated that, while it may be feasible to resettle the
islanders in the short term, the costs of maintaining a long-term inhabita-
tion were likely to be prohibitive. Even in the short term, natural events
such as periodic ﬂooding from storms and seismic activity, were likely to
make life diﬃcult for a resettled population. In 2004, the United King-
dom issued two orders in Council: the British Indian Ocean Territory
(Constitution) Order 2004 and the British Indian Ocean Territory (Immi-
gration) Order 2004. These orders declared that no person had the right
of abode in the BIOT nor the right without authorization to enter and
remain there.
   125. In 2004, Mr. Bancoult challenged the validity of the British Indian
Ocean Territory (Constitution) Order 2004 and the British Indian Ocean
Territory (Immigration) Order 2004 in the courts of the United King-
dom. He succeeded in the High Court. An appeal was brought by the
Secretary of State for Foreign and Commonwealth Aﬀairs against the
decision of the High Court. The Court of Appeal upheld the decision of
the High Court that the orders were invalid on the basis that their content

                                                                           35

             separation of the chagos (advisory opinion)               127

and the circumstances of their adoption constituted an abuse of power by
the United Kingdom Government (Regina (Bancoult) v. Secretary of
State for Foreign and Commonwealth Affairs (No. 2) (2007)).
   126. On 30 July 2008, the Human Rights Committee, in considering
another periodic report submitted by the United Kingdom, took note of
the aforementioned decision of the Court of Appeal. On the basis of Arti-
cle 12 of the International Covenant on Civil and Political Rights, the
Committee recommended that:
       “The State party should ensure that the Chagos islanders can exer-
    cise their right to return to their territory and should indicate what
    measures have been taken in this regard. It should consider compen-
    sation for the denial of this right over an extended period.”

   127. The Secretary of State for Foreign and Commonwealth Aﬀairs
appealed the decision of the Court of Appeal (see paragraph 125) uphold-
ing Mr. Bancoult’s challenge of the validity of the British Indian Ocean
Territory (Constitution) Order 2004. On 22 October 2008, the House of
Lords upheld the appeal by the Secretary of State for Foreign and Com-
monwealth Aﬀairs.
   128. On 11 December 2012, the European Court of Human Rights, in
the Chagos Islanders v. United Kingdom case, declared inadmissible an
application made by a group of 1,786 Chagossians against the
United Kingdom for breach of their rights under the European Conven-
tion on Human Rights. One of the grounds for the decision was that the
claims of the applicants had been settled through implementation of the
1982 Agreement between Mauritius and the United Kingdom.
   129. On 20 December 2012, the United Kingdom announced a review
of its policy on resettlement of the Chagossians who were forcibly
removed from, or prevented from returning to, the Chagos Archipelago.
A second feasibility study, carried out between 2014 and 2015, was com-
missioned by the BIOT Administration to analyse the diﬀerent options
for resettlement in the Chagos Archipelago. The feasibility study con-
cluded that resettlement was possible although there would be signiﬁcant
challenges including high and very uncertain costs, and long-term
liabilities for the United Kingdom taxpayer. Thereafter, on 16 November
2016, the United Kingdom decided against resettlement on the “grounds
of feasibility, defence and security interests and cost to the British tax-
payer”.

  130. On 8 February 2018, the Supreme Court of the United Kingdom
rendered its judgment in the case of Regina (on the application of Ban-
coult No. 3) v. Secretary of State for Foreign and Commonwealth Affairs
(2018). The case was brought by Mr. Bancoult on behalf of a group of
Chagossians who were forcibly removed from the archipelago. In the pro-
ceedings, Mr. Bancoult challenged the declaration of a marine protected
area by the United Kingdom around the Chagos Archipelago. Mr. Ban-

                                                                        36

             separation of the chagos (advisory opinion)               128

coult, the appellant, contended that the marine protected area had been
established for the improper purpose of rendering impracticable the reset-
tlement of the Chagos islanders on the archipelago. He claimed that this
was evidenced by a diplomatic cable sent by the United States Embassy
in London to departments of the United States Government in Washing-
ton, to elements in its military command structure and to its Embassy in
Port Louis, Mauritius. The cable recorded a 2009 meeting in which
United States and United Kingdom oﬃcials discussed the reasons for the
establishment of the marine protected area. The cable was subsequently
leaked and published in two national newspapers. Called upon in the
appeal to rule on the admissibility of that cable, the Supreme Court held
that the cable in question was admissible. However, it dismissed the
appeal on other grounds.
   131. To date, the Chagossians remain dispersed in several countries,
including the United Kingdom, Mauritius and Seychelles. By virtue of
United Kingdom law and judicial decisions of that country, they are not
allowed to return to the Chagos Archipelago.

   IV. The Questions Put to the Court by the General Assembly

  132. Having reviewed the factual background of the present request
for an advisory opinion, the Court will now examine the two questions
put by the General Assembly:
       Question (a): “Was the process of decolonization of Mauritius
    lawfully completed when Mauritius was granted independence
    in 1968, following the separation of the Chagos Archipelago from
    Mauritius and having regard to international law, including obliga-
    tions reﬂected in General Assembly resolutions 1514 (XV) of
    14 December 1960, 2066 (XX) of 16 December 1965, 2232 (XXI) of
    20 December 1966 and 2357 (XXII) of 19 December 1967?”
       Question (b): “What are the consequences under international law,
    including obligations reﬂected in the above-mentioned resolutions,
    arising from the continued administration by the United Kingdom of
    Great Britain and Northern Ireland of the Chagos Archipelago,
    including with respect to the inability of Mauritius to implement a
    programme for the resettlement on the Chagos Archipelago of its
    nationals, in particular those of Chagossian origin?”
   133. Some participants have asked the Court to reformulate both
questions or to interpret them restrictively. In particular, they have con-
tested the assumption that the resolutions referred to in Question (a)
would create international obligations for the United Kingdom, thereby
prejudging the answer the Court is requested to give. They have also con-
tended that the legal questions really at issue concern the matter of
sovereignty over the Chagos Archipelago, which is the subject of a bilat-
eral dispute between Mauritius and the United Kingdom.

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             separation of the chagos (advisory opinion)                  129

   134. One participant has asserted that the General Assembly’s request,
which does not expressly refer to the legal consequences for States of the
continued administration by the United Kingdom of the Chagos
Archipelago, should be interpreted in such a way as to limit the advi-
sory opinion to the functions of the United Nations, excluding all
issues that concern States, in particular, Mauritius and the United King-
dom.
   135. The Court recalls that it may depart from the language of the
question put to it where the question is not adequately formulated (Inter-
pretation of the Greco-Turkish Agreement of 1 December 1926 (Final Pro-
tocol, Article IV), Advisory Opinion, 1928, P.C.I.J., Series B, No. 16) or
does not reﬂect the “legal questions really in issue” (Interpretation of the
Agreement of 25 March 1951 between the WHO and Egypt, Advisory
Opinion, I.C.J. Reports 1980, p. 89, para. 35). Similarly, where the
question asked is ambiguous or vague, the Court may clarify it before
giving its opinion (Application for Review of Judgement No. 273 of the
United Nations Administrative Tribunal, Advisory Opinion, I.C.J. Reports
1982, p. 348, para. 46). Although, in exceptional circumstances, the
Court may reformulate the questions referred to it for an advisory
opinion, it only does so to ensure that it gives a reply “based on
law” (Western Sahara, Advisory Opinion, I.C.J. Reports 1975, p. 18,
para. 15).
   136. The Court considers that there is no need for it to reformulate the
questions submitted to it for an advisory opinion in these proceedings.
Indeed, the ﬁrst question is whether the process of decolonization of
Mauritius was lawfully completed in 1968, having regard to international
law, following the separation of the Chagos Archipelago from its terri-
tory in 1965. The General Assembly’s reference to certain resolutions
which it adopted during this period does not, in the Court’s view, pre-
judge either their legal content or scope. In Question (a), the General
Assembly asks the Court to examine certain events which occurred
between 1965 and 1968, and which fall within the framework of the pro-
cess of decolonization of Mauritius as a non-self-governing territory. It
did not submit to the Court a bilateral dispute over sovereignty which
might exist between the United Kingdom and Mauritius. In Question (b),
which is clearly linked to Question (a), the Court is asked to state the
consequences, under international law, of the continued administration
by the United Kingdom of the Chagos Archipelago. By referring in this
way to international law, the General Assembly necessarily had in mind
the consequences for the subjects of that law, including States.

   137. It is for the Court to state the law applicable to the factual situa-
tion referred to it by the General Assembly in its request for an advisory
opinion. There is thus no need for it to interpret restrictively the questions
put to it by the General Assembly. When the Court states the law in the
exercise of its advisory function, it lends its assistance to the General
Assembly in the solution of a problem confronting it (Western Sahara,

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             separation of the chagos (advisory opinion)                 130

Advisory Opinion, I.C.J. Reports 1975, p. 21, para. 23). In giving its advi-
sory opinion, the Court is not interfering with the exercise of the General
Assembly’s own functions.
  138. The Court will now consider the ﬁrst question put to it by the
General Assembly, namely whether the process of decolonization of
Mauritius was lawfully completed having regard to international law.

               A. Whether the Process of Decolonization
          of Mauritius Was Lawfully Completed Having Regard
                  to International Law (Question (a))
  139. In order to pronounce on whether the process of decolonization
of Mauritius was lawfully completed having regard to international law,
the Court will determine, ﬁrst, the relevant period of time for the purpose
of identifying the applicable rules of international law and, secondly, the
content of that law. In addition, since the General Assembly has referred
to some of the resolutions it adopted, the Court, in determining the obli-
gations reﬂected in these resolutions, will have to examine the functions
of the General Assembly in conducting the process of decolonization.

1. The relevant period of time for the purpose of identifying the applicable
   rules of international law
   140. In Question (a), the General Assembly situates the process of
decolonization of Mauritius in the period between the separation of the
Chagos Archipelago from its territory in 1965 and its independence in
1968. It is therefore by reference to this period that the Court is required
to identify the rules of international law that are applicable to that pro-
cess.
   141. Various participants have stated that international law is not fro-
zen at the date when the ﬁrst steps were taken towards the realization of
the right to self-determination in respect of a territory.
   142. The Court is of the view that, while its determination of the appli-
cable law must focus on the period from 1965 to 1968, this will not pre-
vent it, particularly when customary rules are at issue, from considering
the evolution of the law on self-determination since the adoption of the
Charter of the United Nations and of resolution 1514 (XV) of 14 Decem-
ber 1960 entitled “Declaration on the Granting of Independence to Colo-
nial Countries and Peoples”. Indeed, State practice and opinio juris,
i.e. the acceptance of that practice as law (Article 38 of the Statute of the
Court), are consolidated and conﬁrmed gradually over time.

  143. The Court may also rely on legal instruments which postdate
the period in question, when those instruments conﬁrm or interpret pre-
existing rules or principles.

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             separation of the chagos (advisory opinion)                  131

2. Applicable international law
   144. The Court will have to determine the nature, content and scope of
the right to self-determination applicable to the process of decolonization
of Mauritius, a non-self-governing territory recognized as such, from 1946
onwards, both in United Nations practice and by the administering Power
itself. The Court is conscious that the right to self-determination, as a
fundamental human right, has a broad scope of application. However, to
answer the question put to it by the General Assembly, the Court will
conﬁne itself, in this Advisory Opinion, to analysing the right to self-
determination in the context of decolonization.

   145. The participants in the advisory proceedings have adopted oppos-
ing positions on the customary status of the right to self-determination,
its content and how it was exercised in the period between 1965 and 1968.
Some participants have asserted that the right to self-determination was
ﬁrmly established in customary international law at the time in question.
Others have maintained that the right to self-determination was not an
integral part of customary international law in the period under consider-
ation.
   146. The Court will begin by recalling that “respect for the principle of
equal rights and self-determination of peoples” is one of the purposes of
the United Nations (Article 1, paragraph 2, of the Charter). Such a pur-
pose concerns, in particular, the “Declaration regarding non-self-govern-
ing territories” (Chapter XI of the Charter), since the “Members of the
United Nations which have or assume responsibilities for the administra-
tion of territories whose peoples have not yet attained a full measure of
self-government” are obliged to “develop [the] self-government” of those
peoples (Article 73 of the Charter).

   147. In the Court’s view, it follows that the legal régime of non-self-
governing territories, as set out in Chapter XI of the Charter, was based
on the progressive development of their institutions so as to lead the pop-
ulations concerned to exercise their right to self-determination.
   148. Having made respect for the principle of equal rights and
self-determination of peoples one of the purposes of the United Nations,
the Charter included provisions that would enable non-self-governing ter-
ritories ultimately to govern themselves. It is in this context that the Court
must ascertain when the right to self-determination crystallized as a cus-
tomary rule binding on all States.

  149. Custom is constituted through “general practice accepted as law”
(Article 38 of the Statute of the Court). The Court has emphasized that
both elements, namely general practice and opinio juris, which are consti-
tutive of international custom, are closely linked:
      “Not only must the acts concerned amount to a settled practice,
    but they must also be such, or be carried out in such a way, as to be
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             separation of the chagos (advisory opinion)                  132

    evidence of a belief that this practice is rendered obligatory by the
    existence of a rule of law requiring it. The need for such a belief, i.e.,
    the existence of a subjective element, is implicit in the very notion of
    the opinio juris sive necessitatis. The States concerned must therefore
    feel that they are conforming to what amounts to a legal obligation.
    The frequency, or even habitual character of the acts is not in itself
    enough.” (North Sea Continental Shelf, Judgment, I.C.J. Reports
    1969, p. 44, para. 77.)

   150. The adoption of resolution 1514 (XV) of 14 December 1960 rep-
resents a deﬁning moment in the consolidation of State practice on decol-
onization. Prior to that resolution, the General Assembly had aﬃrmed on
several occasions the right to self-determination (resolutions 637 (VII) of
16 December 1952, 738 (VIII) of 28 November 1953 and 1188 (XII) of
11 December 1957) and a number of non-self-governing territories had
acceded to independence. General Assembly resolution 1514 (XV) clari-
ﬁes the content and scope of the right to self-determination. The Court
notes that the decolonization process accelerated in 1960, with 18 coun-
tries, including 17 in Africa, gaining independence. During the 1960s, the
peoples of an additional 28 non-self-governing-territories exercised their
right to self-determination and achieved independence. In the Court’s
view, there is a clear relationship between resolution 1514 (XV) and the
process of decolonization following its adoption.
   151. As the Court has noted:
    “General Assembly resolutions, even if they are not binding, may
    sometimes have normative value. They can, in certain circumstances,
    provide evidence important for establishing the existence of a rule or
    the emergence of an opinio juris. To establish whether this is true of
    a given General Assembly resolution, it is necessary to look at its
    content and the conditions of its adoption; it is also necessary to see
    whether an opinio juris exists as to its normative character.” (Legality
    of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J.
    Reports 1996 (I), pp. 254-255, para. 70.)
   152. The Court considers that, although resolution 1514 (XV) is for-
mally a recommendation, it has a declaratory character with regard to the
right to self-determination as a customary norm, in view of its content
and the conditions of its adoption. The resolution was adopted by
89 votes with 9 abstentions. None of the States participating in the vote
contested the existence of the right of peoples to self-determination. Cer-
tain States justiﬁed their abstention on the basis of the time required for
the implementation of such a right.
   153. The wording used in resolution 1514 (XV) has a normative char-
acter, in so far as it aﬃrms that “[a]ll peoples have the right to self-
determination”. Its preamble proclaims “the necessity of bringing to a
speedy and unconditional end colonialism in all its forms and manifesta-

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             separation of the chagos (advisory opinion)                  133

tions” and its ﬁrst paragraph states that “[t]he subjection of peoples to
alien subjugation, domination and exploitation constitutes a denial of
fundamental human rights [and] is contrary to the Charter of the
United Nations”.
   This resolution further provides that “[i]mmediate steps shall be taken,
in Trust and Non-Self-Governing Territories or all other territories which
have not yet attained independence, to transfer all powers to the peoples
of those territories, without any conditions or reservations, in accordance
with their freely expressed will and desire”. In order to prevent any dis-
memberment of non-self-governing territories, paragraph 6 of resolu-
tion 1514 (XV) provides that:
      “Any attempt aimed at the partial or total disruption of the national
    unity and the territorial integrity of a country is incompatible with
    the purposes and principles of the Charter of the United Nations.”
  154. Article 1, common to the International Covenant on Civil and
Political Rights and to the International Covenant on Economic, Social
and Cultural Rights, adopted on 16 December 1966, by General Assem-
bly resolution 2200 A (XXI), reaﬃrms the right of all peoples to self-
determination, and provides, inter alia, that:
      “The States Parties to the present Covenant, including those having
    responsibility for the administration of Non-Self-Governing and
    Trust Territories, shall promote the realization of the right of self-
    determination, and shall respect that right, in conformity with the
    provisions of the Charter of the United Nations.”
   155. The nature and scope of the right to self-determination of peo-
ples, including respect for “the national unity and territorial integrity of a
State or country”, were reiterated in the Declaration on Principles of
International Law concerning Friendly Relations and Co-operation
among States in accordance with the Charter of the United Nations. This
Declaration was annexed to General Assembly resolution 2625 (XXV)
which was adopted by consensus in 1970. By recognizing the right to self-
determination as one of the “basic principles of international law”, the
Declaration conﬁrmed its normative character under customary interna-
tional law.
   156. The means of implementing the right to self-determination in a
non-self-governing territory, described as “geographically separate
and . . . distinct ethnically and/or culturally from the country administer-
ing it”, were set out in Principle VI of General Assembly resolu-
tion 1541 (XV), adopted on 15 December 1960:
      “A Non-Self-Governing Territory can be said to have reached a
    full measure of self-government by:
    (a) Emergence as a sovereign independent State;
    (b) Free association with an independent State; or
    (c) Integration with an independent State.”

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              separation of the chagos (advisory opinion)                   134

   157. The Court recalls that, while the exercise of self-determination
may be achieved through one of the options laid down by resolu-
tion 1541 (XV), it must be the expression of the free and genuine will of
the people concerned. However, “[t]he right of self-determination leaves
the General Assembly a measure of discretion with respect to the forms
and procedures by which that right is to be realized” (Western Sahara,
Advisory Opinion, I.C.J. Reports 1975, p. 36, para. 71).
   158. The right to self-determination under customary international law
does not impose a speciﬁc mechanism for its implementation in all
instances, as the Court has observed:
        “The validity of the principle of self-determination, deﬁned as the
     need to pay regard to the freely expressed will of peoples, is not
     aﬀected by the fact that in certain cases the General Assembly has
     dispensed with the requirement of consulting the inhabitants of
     a given territory. Those instances were based either on the consider-
     ation that a certain population did not constitute a ‘people’ entitled
     to self-determination or on the conviction that a consultation was
     totally unnecessary, in view of special circumstances.” (Ibid., p. 33,
     para. 59.)
   159. Some participants have argued that the customary status of the
right to self-determination did not entail an obligation to implement that
right within the boundaries of the non-self-governing territory.
   160. The Court recalls that the right to self-determination of the
people concerned is deﬁned by reference to the entirety of a non-self-
governing territory, as stated in the aforementioned paragraph 6 of
resolution 1514 (XV) (see paragraph 153 above). Both State practice and
opinio juris at the relevant time conﬁrm the customary law character of
the right to territorial integrity of a non-self-governing territory as a corol-
lary of the right to self-determination. No example has been brought to the
attention of the Court in which, following the adoption of resolution 1514
(XV), the General Assembly or any other organ of the United Nations has
considered as lawful the detachment by the administering Power of part
of a non-self-governing territory, for the purpose of maintaining it under
its colonial rule. States have consistently emphasized that respect for the
territorial integrity of a non-self-governing territory is a key element of
the exercise of the right to self-determination under international law.
The Court considers that the peoples of non-self-governing territories are
entitled to exercise their right to self-determination in relation to their ter-
ritory as a whole, the integrity of which must be respected by the admin-
istering Power. It follows that any detachment by the administering
Power of part of a non-self-governing territory, unless based on the freely
expressed and genuine will of the people of the territory concerned, is
contrary to the right to self-determination.

  161. In the Court’s view, the law on self-determination constitutes the
applicable international law during the period under consideration,

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             separation of the chagos (advisory opinion)                 135

namely between 1965 and 1968. The Court noted in its Advisory Opinion
on Namibia the consolidation of that law:
    “the subsequent development of international law in regard to non-
    self-governing territories, as enshrined in the Charter of the
    United Nations, made the principle of self-determination applicable
    to all of them” (Legal Consequences for States of the Continued Pres-
    ence of South Africa in Namibia (South West Africa) notwithstanding
    Security Council Resolution 276 (1970), Advisory Opinion, I.C.J.
    Reports 1971, p. 31, para. 52).
  162. The Court will now examine the functions of the General Assem-
bly during the process of decolonization.

3. The functions of the General Assembly with regard to decolonization

   163. The General Assembly has played a crucial role in the work of the
United Nations on decolonization, in particular, since the adoption of
resolution 1514 (XV). It has overseen the implementation of the obliga-
tions of Member States in this regard, such as they are laid down in
Chapter XI of the Charter and as they arise from the practice which has
developed within the Organization.
   164. It is in this context that the Court is asked in Question (a) to
consider, in its analysis of the international law applicable to the process
of decolonization of Mauritius, the obligations reﬂected in General
Assembly resolutions 2066 (XX) of 16 December 1965, 2232 (XXI) of
20 December 1966 and 2357 (XXII) of 19 December 1967.

   165. In resolution 2066 (XX) of 16 December 1965, entitled “Question
of Mauritius”, having noted “with deep concern that any step taken by
the administering Power to detach certain islands from the Territory of
Mauritius for the purpose of establishing a military base would be in con-
travention of the Declaration, and in particular of paragraph 6 thereof”,
the General Assembly, in the operative part of the text, invites “the
administering Power to take no action which would dismember the Terri-
tory of Mauritius and violate its territorial integrity”.

  166. In resolutions 2232 (XXI) and 2357 (XXII), which are more gen-
eral in nature and relate to the monitoring of the situation in a number of
non-self-governing territories, the General Assembly
    “[r]eiterates its declaration that any attempt aimed at the partial or
    total disruption of the national unity and the territorial integrity of
    colonial Territories and the establishment of military bases and instal-
    lations in these Territories is incompatible with the purposes and prin-
    ciples of the Charter of the United Nations and of General Assembly
    resolution 1514 (XV)”.

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             separation of the chagos (advisory opinion)                  136

   167. In the Court’s view, by inviting the United Kingdom to comply
with its international obligations in conducting the process of decoloniza-
tion of Mauritius, the General Assembly acted within the framework of
the Charter and within the scope of the functions assigned to it to oversee
the application of the right to self-determination. The General Assembly
assumed those functions in order to supervise the implementation of obli-
gations incumbent upon administering Powers under the Charter. It thus
established a special committee tasked with examining the factors that
would enable it to decide “whether any territory is or is not a territory
whose people have not yet attained a full measure of self-government”
(resolution 334 (IV) of 2 December 1949). It has been the Assembly’s con-
sistent practice to adopt resolutions to pronounce on the speciﬁc situation
of any non-self-governing territory. Thus, immediately after the adoption
of resolution 1514 (XV), it established the Committee of Twenty-Four
tasked with monitoring the implementation of that resolution and mak-
ing suggestions and recommendations thereon (resolution 1654 (XVI) of
27 November 1961). The General Assembly also monitors the means by
which the free and genuine will of the people of a non-self-governing ter-
ritory is expressed, including the formulation of questions submitted for
popular consultation.

  168. The General Assembly has consistently called upon administering
Powers to respect the territorial integrity of non-self-governing territories,
especially after the adoption of resolution 1514 (XV) of 14 December
1960 (see, for example, General Assembly resolutions 2023 (XX) of
5 November 1965 and 2183 (XXI) of 12 December 1966 (Question
of Aden); 3161 (XXVIII) of 14 December 1973 and 3291 (XXIX) of
13 December 1974 (Question of the Comoro Archipelago); 34/91 of
12 December 1979 (Question of the islands of Glorieuses, Juan de Nova,
Europa and Bassas da India)).
  169. The Court will now examine the circumstances relating to
the detachment of the Chagos Archipelago from Mauritius and
determine whether it was carried out in accordance with international
law.

4. Application in the present proceedings
   170. It is necessary to begin by recalling the legal status of Mauritius
before its independence. Following the conclusion of the 1814 Treaty
of Paris, the “island of Mauritius and the Dependencies of Mauritius”
[“l’île Maurice et les dépendances de Maurice”], including the Chagos
Archipelago, were administered without interruption by the United
Kingdom. This is how the whole of Mauritius, including its depen-
dencies, came to appear on the list of non-self-governing territories
drawn up by the General Assembly (resolution 66 (I) of 14 December
1946). It was on this basis that the United Kingdom regularly
provided the General Assembly with information relating to the

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             separation of the chagos (advisory opinion)               137

existing conditions in that territory, in accordance with Article 73 of the
Charter. Therefore, at the time of its detachment from Mauritius in 1965,
the Chagos Archipelago was clearly an integral part of that non-self-
governing territory.
   171. In the Lancaster House agreement of 23 September 1965, the Pre-
mier and other representatives of Mauritius, which was still under the
authority of the United Kingdom as administering Power, agreed in prin-
ciple to the detachment of the Chagos Archipelago from the territory of
Mauritius. This agreement in principle was given on condition that the
archipelago could not be ceded to any third party and would be returned
to Mauritius at a later date, a condition which was accepted at the time
by the United Kingdom.
   172. The Court observes that when the Council of Ministers agreed in
principle to the detachment from Mauritius of the Chagos Archipelago,
Mauritius was, as a colony, under the authority of the United Kingdom.
As noted at the time by the Committee of Twenty-Four: “the present
Constitution of Mauritius . . . do[es] not allow the representatives of the
people to exercise real legislative or executive powers, and that authority
is nearly all concentrated in the hands of the United Kingdom Govern-
ment and its representatives” (UN doc. A/5800/Rev.1 (1964-1965), p. 352,
para. 154). In the Court’s view, it is not possible to talk of an interna-
tional agreement, when one of the parties to it, Mauritius, which is said
to have ceded the territory to the United Kingdom, was under the author-
ity of the latter. The Court is of the view that heightened scrutiny should
be given to the issue of consent in a situation where a part of a non-self-
governing territory is separated to create a new colony. Having reviewed
the circumstances in which the Council of Ministers of the colony of
Mauritius agreed in principle to the detachment of the Chagos Archipel-
ago on the basis of the Lancaster House agreement, the Court considers
that this detachment was not based on the free and genuine expression of
the will of the people concerned.

   173. In its resolution 2066 (XX) of 16 December 1965, adopted a few
weeks after the detachment of the Chagos Archipelago, the General
Assembly deemed it appropriate to recall the obligation of the
United Kingdom, as the administering Power, to respect the territorial
integrity of Mauritius. The Court considers that the obligations arising
under international law and reﬂected in the resolutions adopted by the
General Assembly during the process of decolonization of Mauritius
require the United Kingdom, as the administering Power, to respect the
territorial integrity of that country, including the Chagos Archipelago.

  174. The Court concludes that, as a result of the Chagos Archipelago’s
unlawful detachment and its incorporation into a new colony, known as
the BIOT, the process of decolonization of Mauritius was not lawfully
completed when Mauritius acceded to independence in 1968.

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             separation of the chagos (advisory opinion)                 138

B. The Consequences under International Law arising from the Continued
   Administration by the United Kingdom of the Chagos Archipelago
                           (Question (b))
   175. Having established that the process of decolonization of Mauri-
tius was not lawfully completed in 1968, the Court must now examine the
consequences, under international law, arising from the United King-
dom’s continued administration of the Chagos Archipelago (Ques-
tion (b)). The Court will answer this question, drafted in the present
tense, on the basis of the international law applicable at the time its opin-
ion is given.
   176. Several participants in the proceedings before the Court have
argued that the United Kingdom’s continued administration of the Cha-
gos Archipelago has consequences under international law not only for
the United Kingdom itself, but also for other States and international
organizations. The consequences mentioned include the requirement for
the United Kingdom to put an immediate end to its administration of the
Chagos Archipelago and return it to Mauritius. Some participants have
gone further, advocating that the United Kingdom must make good the
injury suﬀered by Mauritius. Others have considered that the former
administering Power must co-operate with Mauritius regarding the reset-
tlement on the Chagos Archipelago of the nationals of the latter, in par-
ticular those of Chagossian origin.
   In contrast, one participant has contended that the only consequence
for the United Kingdom under international law concerns the retroces-
sion of the Chagos Archipelago when it is no longer needed for the
defence purposes of that State. Finally, a few participants have taken the
view that the time frame for completing the decolonization of Mauritius
is a matter for bilateral negotiations to be conducted between Mauritius
and the United Kingdom.
   As regards the consequences for third States, some participants have
maintained that those States have an obligation not to recognize the
unlawful situation resulting from the United Kingdom’s continued
administration of the Chagos Archipelago and not to render assistance in
maintaining it.

                                    * *
   177. The Court having found that the decolonization of Mauritius was
not conducted in a manner consistent with the right of peoples to
self-determination, it follows that the United Kingdom’s continued
administration of the Chagos Archipelago constitutes a wrongful act
entailing the international responsibility of that State (see Corfu Channel
(United Kingdom v. Albania), Merits, Judgment, I.C.J. Reports 1949,
p. 23; Gabčíkovo-Nagymaros Project (Hungary/Slovakia), Judgment,
I.C.J. Reports 1997, p. 38, para. 47; see also Article 1 of the Articles on
Responsibility of States for Internationally Wrongful Acts). It is an

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             separation of the chagos (advisory opinion)                 139

unlawful act of a continuing character which arose as a result of the sepa-
ration of the Chagos Archipelago from Mauritius.
   178. Accordingly, the United Kingdom is under an obligation to bring
an end to its administration of the Chagos Archipelago as rapidly as
possible, thereby enabling Mauritius to complete the decolonization of
its territory in a manner consistent with the right of peoples to self-
determination.
   179. The modalities necessary for ensuring the completion of the
decolonization of Mauritius fall within the remit of the United Nations
General Assembly, in the exercise of its functions relating to decoloniza-
tion. As the Court has stated in the past, it is not for it to “determine
what steps the General Assembly may wish to take after receiving the
Court’s opinion or what eﬀect that opinion may have in relation to those
steps” (Accordance with International Law of the Unilateral Declaration of
Independence in Respect of Kosovo, Advisory Opinion, I.C.J. Reports
2010 (II), p. 421, para. 44).
   180. Since respect for the right to self-determination is an obligation
erga omnes, all States have a legal interest in protecting that right (see
East Timor (Portugal v. Australia), Judgment, I.C.J. Reports 1995, p. 102,
para. 29; see also Barcelona Traction, Light and Power Company, Limited
(New Application: 1962) (Belgium v. Spain), Second Phase, Judgment,
I.C.J. Reports 1970, p. 32, para. 33). The Court considers that, while it is
for the General Assembly to pronounce on the modalities required to
ensure the completion of the decolonization of Mauritius, all Member
States must co-operate with the United Nations to put those modalities
into eﬀect. As recalled in the Declaration on the Principles of Interna-
tional Law concerning Friendly Relations and Co-operation among
States in accordance with the Charter of the United Nations:

       “Every State has the duty to promote, through joint and separate
    action, realization of the principle of equal rights and self-determina-
    tion of peoples, in accordance with the provisions of the Charter, and
    to render assistance to the United Nations in carrying out the respon-
    sibilities entrusted to it by the Charter regarding the implementation
    of the principle” (General Assembly resolution 2625 (XXV)).

   181. As regards the resettlement on the Chagos Archipelago of Mauri-
tian nationals, including those of Chagossian origin, this is an issue relat-
ing to the protection of the human rights of those concerned, which
should be addressed by the General Assembly during the completion of
the decolonization of Mauritius.
   182. In response to Question (b) of the General Assembly, relating to
the consequences under international law that arise from the continued
administration by the United Kingdom of the Chagos Archipelago, the
Court concludes that the United Kingdom has an obligation to bring to
an end its administration of the Chagos Archipelago as rapidly as possi-

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             separation of the chagos (advisory opinion)                140

ble, and that all Member States must co-operate with the United Nations
to complete the decolonization of Mauritius.

                                      *
                                  *       *

  183. For these reasons,
  The Court,
  (1) Unanimously,
  Finds that it has jurisdiction to give the advisory opinion requested;
  (2) By twelve votes to two,
  Decides to comply with the request for an advisory opinion;
  in favour: President Yusuf; Vice-President Xue; Judges Abraham, Bennouna,
     Cançado Trindade, Gaja, Sebutinde, Bhandari, Robinson, Gevorgian,
     Salam, Iwasawa;
  against: Judges Tomka, Donoghue;
  (3) By thirteen votes to one,
  Is of the opinion that, having regard to international law, the process of
decolonization of Mauritius was not lawfully completed when that
country acceded to independence in 1968, following the separation of the
Chagos Archipelago;
  in favour: President Yusuf; Vice-President Xue; Judges Tomka, Abraham,
    Bennouna, Cançado Trindade, Gaja, Sebutinde, Bhandari, Robinson,
    Gevorgian, Salam, Iwasawa;
  against: Judge Donoghue;
  (4) By thirteen votes to one,
  Is of the opinion that the United Kingdom is under an obligation to
bring to an end its administration of the Chagos Archipelago as rapidly
as possible;
  in favour: President Yusuf; Vice-President Xue; Judges Tomka, Abraham,
    Bennouna, Cançado Trindade, Gaja, Sebutinde, Bhandari, Robinson,
    Gevorgian, Salam, Iwasawa;
  against: Judge Donoghue;
  (5) By thirteen votes to one,
   Is of the opinion that all Member States are under an obligation to
co-operate with the United Nations in order to complete the decoloniza-
tion of Mauritius.
  in favour: President Yusuf; Vice-President Xue; Judges Tomka, Abraham,
    Bennouna, Cançado Trindade, Gaja, Sebutinde, Bhandari, Robinson,
    Gevorgian, Salam, Iwasawa;
  against: Judge Donoghue.

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            separation of the chagos (advisory opinion)             141

  Done in French and in English, the French text being authoritative, at
the Peace Palace, The Hague, this twenty-ﬁfth day of February, two
thousand and nineteen, in two copies, one of which will be placed in the
archives of the Court and the other transmitted to the Secretary-General
of the United Nations.

                                 (Signed) Abdulqawi Ahmed Yusuf,
                                                 President.
                                     (Signed) Philippe Couvreur,
                                                   Registrar.

  Vice-President Xue appends a declaration to the Advisory Opinion of
the Court; Judges Tomka and Abraham append declarations to the Advi-
sory Opinion of the Court; Judge Cançado Trindade appends a separate
opinion to the Advisory Opinion of the Court; Judges Cançado Trin-
dade and Robinson append a joint declaration to the Advisory Opinion
of the Court; Judge Donoghue appends a dissenting opinion to the Advi-
sory Opinion of the Court; Judges Gaja, Sebutinde and Robinson
append separate opinions to the Advisory Opinion of the Court;
Judges Gevorgian, Salam and Iwasawa append declarations to the
Advisory Opinion of the Court.

                                                  (Initialled) A.A.Y.
                                                   (Initialled) Ph.C.

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