Chagos Archipelago

The Chagos Archipelago (/ˈtʃɑːɡəs, -ɡoʊs/) or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives archipelago. This chain of islands is the southernmost archipelago of the Chagos–Laccadive Ridge, a long submarine mountain range in the Indian Ocean. In its north are the Salomon Islands, Nelsons Island and Peros Banhos; towards its south-west are the Three Brothers, Eagle Islands, Egmont Islands and Danger Island; southeast of these is Diego Garcia, by far the largest island. All are low-lying atolls, save for a few extremely small instances, set around lagoons.
The Chagos Islands had been home to the Chagossians, a Bourbonnais Creole-speaking people, until the United Kingdom expelled them from the archipelago at the request of the United States between 1967 and 1973 to allow the United States to build Naval Support Facility Diego Garcia, a military base on Diego Garcia, on land leased from the UK military in the British Indian Ocean Territories. Since 1971, only the atoll of Diego Garcia has been inhabited, and only by employees of the US military, including American civilian contracted personnel. Since being expelled, Chagossians, like all others not permitted by the UK or US governments, have been prevented from entering the islands.
From 1715 to 1810, the Chagos Islands were part of France's Indian Ocean possessions, administered through Isle de France - which was a colony of France (later renamed as Mauritius). Under the Treaty of Paris (1814), France ceded Isle de France and the Chagos Islands to the United Kingdom.
In 1965, the United Kingdom split the Chagos Archipelago away from Mauritius, and the islands of Aldabra, Farquhar, and Desroches from the Seychelles, to form the British Indian Ocean Territory. The islands were formally established as an overseas territory of the United Kingdom on 8 November 1965. During UK-US discussions on the Indian Ocean in November 1975, the United Kingdom expressed its intention to return the islands of Aldabra, Farquhar, and Desroches to Seychelles to facilitate its peaceful transition to independence by June 1976. Both the UK and the United States acknowledged that these islands could not be used for defense purposes, as they were populated, and forcibly removing inhabitants, as had occurred in the Chagos Archipelago, would be politically unfeasible. On 18 March 1976, the UK and Seychelles signed an agreement to transfer the islands, which officially returned to Seychelles on its Independence Day, 29 June 1976. The British Indian Ocean Territory now comprises the Chagos Archipelago only.
Between 1967 and 1973, the entire population of the Chagos Archipelago was either prevented from returning or forcibly removed by the United Kingdom. The main forcible removal of Diego Garcia’s population took place in July and September 1971. Mauritius has since been engaged in a sovereignty dispute with the UK, claiming the Chagos Archipelago as part of Mauritius.
In 2004, the UK amended its exclusion clause to block Mauritius from taking the Chagos dispute to the International Court of Justice. This move ensured that even if Mauritius left the Commonwealth, it could not challenge the UK in court.
On 18 March 2015, the Permanent Court of Arbitration ruled that the UK's marine protected area around the Chagos Archipelago violated international law. The tribunal upheld Mauritius' sovereignty claims, rejecting the UK's argument and affirming its binding commitments on fishing and mineral rights.
On 23 June 2017, the UN General Assembly voted to refer the Chagos dispute to the International Court of Justice, which began hearings in 2018. While 17 countries backed Mauritius, the UK insisted the issue should be resolved through bilateral talks. In 2019, the International Court of Justice (ICJ) issued a non-binding advisory opinion stating that the UK "has an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible, and that all Member States must co-operate with the United Nations to complete the decolonization of Mauritius".
In 2021, the International Tribunal for the Law of the Sea confirmed for its jurisdiction, in a binding ruling, that the UK has "no sovereignty over the Chagos Islands", and thus the islands should be handed back to Mauritius.
In August 2021, the Universal Postal Union banned BIOT stamps from being used in the BIOT, a move Mauritian Prime Minister Pravind Jugnauth called a "big step in favour of the recognition of the sovereignty of Mauritius over the Chagos".
In October 2024, the British government announced it would hand over sovereignty of the Chagos Islands to Mauritius subject to finalisation of a treaty. The Chagossian people living in the UK have criticised the deal for not having included the Chagossian community in the decision-making process. A segment of the Chagossian community, particularly those with British citizenship residing in the UK, favor continued British sovereignty over the Chagos Archipelago, expressing concerns that their interests may not be fully safeguarded under Mauritian administration. However, many Chagossians, including those in Mauritius, support Mauritian sovereignty. The Chagos Refugees Group, the largest Chagossian advocacy organization, has been a leading voice for this position. Its leader, Olivier Bancoult, described the UK's decision to return the Chagos Archipelago to Mauritius and allow Chagossians to resettle on the outer islands as a significant step and an acknowledgment of past injustices. The deal was put on hold following the 2024 United States presidential election to allow consideration from the new incoming administration. On 27 February 2025, speaking in the Oval Office alongside Prime Minister Sir Keir Starmer, U.S. President Donald Trump stated that he was willing to support the agreement to transfer sovereignty of the Chagos Islands to Mauritius.
The archipelago is about 500 kilometres (310 mi) south of the Maldives, 1,880 kilometres (1,170 mi) east of the Seychelles, 1,680 kilometres (1,040 mi) north-east of Rodrigues Island (Mauritius), 2,700 kilometres (1,700 mi) west of the Cocos (Keeling) Islands, and 3,400 kilometres (2,100 mi) north of Amsterdam Island.
The land area of the islands is 56.1 km (21.7 sq mi), the largest island, Diego Garcia, having an area of 32.5 km (12.5 sq mi). The total area, including lagoons within atolls, is more than 15,000 km (5,800 sq mi), of which 12,642 km (4,881 sq mi) are accounted by the Great Chagos Bank, the largest acknowledged atoll structure of the world (the completely submerged Saya de Malha Bank is larger, but its status as an atoll is uncertain). The shelf area is 20,607 km (7,956 sq mi), and the Exclusive Economic Zone, which borders the corresponding zone of the Maldives in the north, has an area of 639 km (247 sq mi) (including territorial waters).
The Chagos group is a combination of different coralline rock structures topping a submarine ridge running southwards across the centre of the Indian Ocean, formed by volcanoes above the Réunion hotspot. Unlike the Maldives, there is no clearly discernible pattern in the atoll arrangement, which makes the whole archipelago look somewhat chaotic. Most of the coralline structures of the Chagos are submerged reefs.
The Chagos contain the world's largest coral atoll, The Great Chagos Bank, which supports half the total area of good quality reefs in the Indian Ocean. As a result, the ecosystems of the Chagos have so far proven resilient to climate change and environmental disruptions.
The largest individual islands are Diego Garcia (32.5 km (12.5 sq mi)), Eagle (Great Chagos Bank, 3.1 km (1.2 sq mi)), Île Pierre (Peros Banhos, 1.4 km (0.54 sq mi)), Eastern Egmont (Egmont Islands, 2.175 km (0.840 sq mi)), Île du Coin (Peros Banhos, 1.32 km (0.51 sq mi)) and Île Boddam (Salomon Islands, 1.27 km (0.49 sq mi)).
In addition to the seven atolls with dry land reaching at least the high-water mark, there are nine reefs and banks, most of which can be considered permanently submerged atoll structures. The number of atolls in the Chagos Archipelago is given as four or five in most sources, plus two island groups and two single islands, mainly because it is not recognised that the Great Chagos Bank is a huge atoll structure (including those two island groups and two single islands), and because Blenheim Reef, which has islets or cays above or just reaching the high-water mark, is not included. Features are listed in the table from north to south:
The main natural resources of the area are coconuts and fish. The licensing of commercial fishing used to provide an annual income of about US$2 million for the British Indian Ocean Territory authorities. However, licenses have not been given since October 2010; the last expired after the creation of the no-take marine reserve.
All economic activity is concentrated on the largest island of Diego Garcia, where joint UK–US military facilities are located. Construction projects and various services needed to support the military installations are done by military and contract employees from the UK, Mauritius, the Philippines, and the US. There are currently no industrial or agricultural activities on the islands. All the water, food and other essentials of daily life are shipped to the island. An independent feasibility study led to the conclusion that resettlement would be "costly and precarious". Another feasibility study, commissioned by organisations supporting resettlement, found that resettlement would be possible at a cost to the British taxpayer of £25 million. If the Chagossians return, they plan to re-establish copra production and fishing, and to begin the commercial development of the islands for tourism.
Until October 2010, Skipjack (Euthynnus pelamis) and yellowfin tuna (Thunnus albacares) were fished for about two months of the year as their year-long migratory route takes them through Chagos waters. While the remoteness of the Chagos offers some protection from extractive activities, legal and illegal fishing have had an impact. There is considerable poaching of turtles and other marine life. Sharks, which play a vital role in balancing the food web of tropical reefs, have suffered sharp declines from illegal fishing for their fins and as bycatch in legal fisheries. Sea cucumbers, which cleanse sand, are poached to feed Asian markets.
The Chagos Archipelago has a tropical oceanic climate; hot and humid but moderated by trade winds. Climate is characterised by plenty of sunshine, warm temperatures, showers and light breezes. December through February is considered the rainy season (summer monsoon); typical weather conditions include light west-northwesterly winds and warmer temperatures with more rainfall. June to September is considered the drier season (winter), characterised by moderate south-easterly winds, slightly cooler temperatures and less rainfall. The annual mean rainfall is 2 600 mm (100 inches), varying from 105 mm (4 inches) during August to 350 mm (14 inches) during January.
According to Southern Maldivian oral tradition, local traders and fishermen were occasionally lost at sea and became stranded in one of the islands of the Chagos. Eventually they were rescued and brought back home. However, these islands were judged to be too far away from the Maldives to be settled permanently by Maldivians. Thus, for many centuries, the Chagos were ignored by their northern neighbours. However, these tales contrast with the historical view that the Maldives has towards the Chagos, as they were considered to be an extension of Maldivian maritime territory. For centuries, the Maldivians have used the Chagos as a base for fishing expeditions. People would camp on the islands, catch fish, and cook, smoke, and dry them. Additionally, the exiled Maldive King Hassan IX (also known as Dom Manoel), while in Cochin, describes himself in his letters patent of 1561 as King of the Maldive islands, including seven of the islands of Pullobay, referring to Fōlhavahi or the Chagos, and this letter survives in a Portuguese archive in Lisbon.
In Maldivian lore the whole group is known as Fōlhavahi or Hollhavai (Dhivehi: ފޯޅަވަހި or ހޮއްޅަވައި) (the latter name in the Southern Maldives Adduan dialect of Dhivehi). There are no separate names for the different atolls of the Chagos in the Maldivian oral tradition; "Fayhandheeb" is used for the Archipelago as a whole. According to Maldivian history, the Maldives Archipelago consists of Mahaldheeb, Suvaadheebu and Feyhandheeb.
The first Europeans to become aware of the archipelago were Portuguese explorers. Although the Portuguese navigator Pedro de Mascarenhas (1470 – 23 June 1555) is credited with having encountered the islands during his voyage of 1512–13, there is little corroborative evidence; cartographic analysis points to 1532 or later. Portuguese seafarers named the group Bassas de Chagas, Portuguese: Chagas (wounds) referring to the Holy Wounds of the crucifixion of Jesus. They also named some of the atolls, such as Diego Garcia and Peros Banhos Atoll, mentioned as Pedro dos Banhos in 1513 by Afonso de Albuquerque. This lonely and isolated group, economically and politically uninteresting to the Portuguese, was never made part of the Portuguese Empire.
The earliest and most interesting description of the Chagos, before coconut trees grew widely on the islands, was written by Manoel Rangel, a castaway from the Portuguese ship Conceição which ran aground on the Peros Banhos reefs in 1556.
The oldest known written document claiming the Chagos is attributed to King Hassan IX of the Maldives in the year 1561. The French were the first European colonial power to lay claim to the Chagos after they settled Île Bourbon (now Réunion, in 1665) and Isle de France (now Mauritius, in 1715). The French began issuing permits for companies to establish coconut oil plantations on the Chagos in the 1770s.
On 27 April 1786 the Chagos Islands and Diego Garcia were claimed for Great Britain. However, the territory was ceded to Britain by treaty only after Napoleon's defeat, in 1815. The Chagos were governed from Mauritius, which was by that time also a British colony.
In 1793, when the first successful colony was founded on Diego Garcia, the largest island, coconut plantations were established on many of the atolls and isolated islands of the archipelago. The workers were enslaved by the British and not freed until 1840, after which time many of the workers descended from those who had earlier been enslaved. They formed an inter-island culture called Ilois, a French Creole word meaning "Islanders".
Commander Robert Moresby made a survey of the Chagos on behalf of the British Admiralty in 1837–38. After Moresby had taken measurements of most of the atolls and reefs, the archipelago was charted with relative precision for the first time.
Moresby's survey of the Atolls of the Maldives was followed by the Chagos Archipelago.(1854)
Robert Moresby (1794–1854) was a captain of the East India Company's Bombay Marine/Indian Navy who distinguished himself as a hydrographer, maritime surveyor and draughtsman. Moresby is best known for conducting the first modern survey of the Red Sea (1829–32).
After the completion of the Red Sea Survey, Robert Moresby was sent to chart various coral island groups lying across the track of India-to-Cape trade. In 1834–36 Moresby, assisted by Lieutenants Christopher and Young, undertook the difficult cartography of the Maldive Islands, drawing the first accurate maritime charts of this complicated Indian Ocean atoll group (Admiralty Charts). These charts were printed as three separate large maps by the Hydrographic Service of the Royal Navy.
Moresby's survey of the Atolls of the Maldives was followed by the Chagos Archipelago. where he conducted "a thorough scientific survey". He planted 30 breadfruit trees in Diego Garcia Island, the largest of the group. Moresby reported that "there were cats and chickens on the island". Some of his observations were used by Darwin in his 1842 book "The Structure and Distribution of Coral Reefs."
Moresby's charts were so good that they were favored by Maldivian pilots navigating through the treacherous waters of their atolls until the 1990s, when satellite images appeared. In the Maldives a channel locally also known as Hanikandu, between Northern Maalhosmadulhu Atoll and "Fasdhūtere" Atoll, is still known as 'Moresby Channel'.
The British expelled the Dutch from Ceylon in 1796 and included Maldives as a protected state. By the 1800s, the European Oriental Trade had expanded vastly, and since the Maldives straddles the trade routes from Europe and Africa to the East, surveying and charting the Maldivian seas became a most urgent international need. Therefore, when the British Admiralty survey of the Red Sea was completed in 1834, Commander Moresby was dispatched to the Maldives.
Moresby came to the Maldives in 1835 with special letters to the Radhun from the Governments of Bombay and Ceylon. The purpose of Commander Moresby's visit was to survey and chart the Maldivian seas for the British Admiralty. However, the Radhun viewed Moresby's visit with suspicion. Moresby was bearing a letter from the British government to the Radhun. The letter stated that the survey and charting the reefs, sand banks and the depths of the local seas would facilitate the movements of vessels calling at Male', and thereby increase and broaden the local overseas trade. However, when considered in a different perspective there were innumerable issues which could arise because of the British intentions. The reefs and the shallows of the Maldives was her first line of defense. The strategic importance of the topography of the Maldivian reefs, shallows, islands and the atolls of the country has been a closely guarded secret of the Maldivian militia for centuries.
Therefore, if the Maldivian territory was to be charted by the British, this first line of the Maldivian defense system would become obsolete. Mueenuhdeen Radhun's defense system would have been made vulnerable. The Radhun worked to prevent Moresby from his survey work, as it represented a threat to the Radhun's throne. Furthermore, Moresby's inspection of the bastions of Male gave further threat to the Radhun, making the Radhun suspicious of the British intentions. The Radhun not only refused to cooperate with Commander Moresby, but also created all sorts of passive obstructions and Moresby left the Maldives with his intentions unfulfilled.
Ultimately, the situation caused a significant internal political struggle between the Radhun and his rivals, but Moresby was able to complete the first modern survey of the region.
Unauthorized Survey Sparks Tension
One of the most significant incidents occurred in 1834 when Captain Moresby, commissioned by the British East India Company, conducted a survey of the Maldivian archipelago without explicit permission from the local authorities. This unauthorized action, viewed with suspicion and fear by the Maldivian people, highlighted the growing British interest in the region.
The Role of Pro-British Figures
To further their colonial ambitions, the British often supported pro-British figures like Ahmad Dídí, who held considerable influence over Maldivian politics. By backing such individuals, the British were able to indirectly shape the country's policies and decisions.
Exploiting Legal Loopholes
The absence of a formal legal framework and defined borders in the Maldives provided an opportunity for the British to redraw the map of the archipelago to suit their strategic interests. One notable example is the exclusion of the Chagos Archipelago from the Maldivian territory, a decision that continues to have geopolitical implications.
The Enduring Impact
The British colonial legacy, including the imposed map and borders, has had long-lasting consequences for the Maldives. The country continues to grapple with the challenges of asserting its sovereignty and territorial rights, particularly in the context of maritime disputes and resource management.
On 31 August 1903 the Chagos Archipelago was administratively separated from the Seychelles and attached to Mauritius.
Before granting independence to Mauritius, the United Kingdom paid £3 million in compensation to the Mauritius Government and made several undertakings regarding the future status of the Chagos Archipelago. These included a commitment that the archipelago would be returned to Mauritius if it was no longer needed for defence purposes, assurances that Mauritius would retain access to navigational and meteorological facilities as well as fishing rights, and an agreement that any benefits from minerals or oil discovered in or near the Chagos Archipelago would revert to Mauritius. The compensation was intended to support development projects and address the resettlement of the displaced Chagossian community, though its adequacy and distribution have remained subjects of controversy. Various press articles have wrongly suggested that the £3 million payment was for the purchase of the islands from Mauritius, when in fact it was compensation tied to the detachment of the archipelago and broader commitments made by the British government.
On 25 May 1967, less than two years after the agreement with Premier Seewoosagur Ramgoolam, Prime Minister Harold Wilson attended a Cabinet Committee meeting alongside the Chancellor of the Exchequer and the Secretaries of State for Commonwealth Affairs, Economic Affairs, Defence, and the Home Department. During this meeting, the Commonwealth Secretary noted that at the time of the 1965 agreement, Mauritian ministers were unaware of Britain's negotiations with the United States for a financial contribution toward the compensation. Mauritian officials were also informed that there would be no additional contribution from the United States, as this was a matter solely between the U.K. and Mauritius. The British government made it clear that the £3 million was the maximum it could afford and that if Mauritius did not accept the proposal, the U.K. would not proceed with arrangements for granting independence.
During the same meeting, the Secretary of State for Defence stated that when the British Indian Ocean Territory was established, the U.K. had arranged compensation for both Mauritius and the Seychelles for the detachment of islands, with a total budget of approximately £10 million. The United States had agreed to contribute up to half of this amount, with a maximum of £5 million. To avoid potential embarrassment in the U.S. Congress, the U.S. government requested that its financial contribution remain secret. As a result, it was arranged that the U.S. contribution would be concealed by waiving certain payments owed by the U.K. to the U.S. in connection with the development of the Polaris missile program.
On 30 December 1966, the United States and the United Kingdom executed an agreement through an Exchange of Notes which permit the United States Armed Forces to use any island of the BIOT for defence purposes for 50 years, until December 2016, followed by a 20-year optional extension (to 2036) to which both parties must agree by December 2014. As of 2010, only the atoll of Diego Garcia has been transformed into a military facility.
In 1967 the British Government bought the entire assets and real property of the Seychellois Chagos Agalega Company, which owned all the islands of the BIOT, for £660,000 and administered them as a government enterprise while awaiting US funding of its proposed facilities, with an interim objective of paying for the administrative expenses of the new territory. The plantations, under their previous private ownership and under government administration, proved consistently unprofitable due to the introduction of new oils and lubricants in the international marketplace and the establishment of vast coconut plantations in the East Indies and the Philippines.
Between 1967 and 1973, the population was forcibly removed from the islands and moved to Mauritius and the Seychelles to make way for a joint United States–United Kingdom military base on Diego Garcia. In March 1971, United States naval construction battalions (Seabees), arrived on Diego Garcia to begin the construction of the Communications Station and an airfield. To satisfy the terms of an agreement between the United Kingdom and the United States for an uninhabited island, the plantation on Diego Garcia was closed in October of that year.
The plantation workers and their families were initially deported to the plantations on Peros Banhos and Salomon atolls in the group; those who requested were transported to the Seychelles or Mauritius. In 1972, the UK closed the remaining plantations (all being now uneconomic) of the Chagos, and deported the Ilois who would have faced economic hardship to the Seychelles or Mauritius. The independent Mauritian government refused to accept these further displaced islanders without payment and in 1973, the United Kingdom agreed and gave them an additional £650,000 as reparation payments to resettle the people. Some people were of the view that they were rehoused and employed under worse conditions than other Mauritians. The islands were becoming costly to live in due to industrial moves away from coconut oils and copra fibre markets and the success of larger plantations in the far east.
In 2002, Diego Garcia was used twice for US rendition flights.
On 13 October 2009, the Cabinet of the Maldives Government decided to see if the Maldives can claim for an extended continental shelf.
On 26 July 2010, the Republic of Maldives submitted to the Commission on the Limits of the Continental Shelf, in accordance with Article 76, paragraph 8, of the United Nations Convention on the Law of the Sea, information on the limits of the continental shelf beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured.
On 1 April 2010, the British government announced the establishment of the Chagos Marine Protected Area as the world's largest marine reserve. At 640,000 km, it is larger than France or the U.S. state of California. It doubled the total area of environmental no-take zones worldwide. On 18 March 2015, the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) which the United Kingdom declared around the Chagos Archipelago in April 2010 violates international law. Anerood Jugnauth, Prime Minister of Mauritius, pointed out that it is the first time that the United Kingdom's conduct with regard to the Chagos Archipelago has been considered and condemned by any international court or tribunal.
On 20 December 2010 Mauritius initiated proceedings against the United Kingdom under the United Nations Convention on the Law of the Sea (UNCLOS) to challenge the legality of the Chagos Archipelago MPA.
The issue of compensation and repatriation of the former inhabitants of several of the archipelago's atolls, exiled since 1973, continued in litigation, and in 2010 it was submitted to the European Court of Human Rights by a group of former residents.
Litigation continued in 2012 regarding the right of return for the displaced islanders and Mauritian sovereignty claims. In addition, advocacy on the Chagossians' behalf continues both in the United States and in Europe. In 2018, Mauritius took the matter to the International Court of Justice for an advisory opinion, against British objections.
In 2014, a Feasibility Study for the Resettlement of the British Indian Ocean Territory was undertaken by the UK Government by consultants from KPMG.
The objectives of the study were to assess costs and sustainability of resettlement over five, ten, and twenty years, evaluate economic self-sufficiency, risks, and environmental implications, explore potential resettlement options ranging from small-scale pilot projects to larger-scale resettlements.
A neutral analysis was undertaken, including consultations with the Chagossian community and environmental assessments. Options considered included modern lifestyles, subsistence living, eco-villages, and research stations. Legal, environmental, infrastructure, and economic aspects were analysed.
Large-scale resettlement (1,500 people), medium-scale (500 people), and a pilot scheme (150 people) were proposed. Diego Garcia was a preferred location due to existing infrastructure, with Ile du Coin and Boddam also being provisional initial candidate sites.
Chagossians expressed a strong preference for permanent resettlement, not temporary visits. They emphasized the need for modern living standards, environmental conservation, and access to UK-level education and healthcare.
Most islands are low-lying and vulnerable to climate change, with varying suitability for habitation. Environmental protections and monitoring would be critical.
Employment opportunities could include tourism, fishing, and environmental monitoring. High-end and eco-tourism were seen as potential revenue generators.
Amendments to BIOT's legal framework would be required to facilitate resettlement. Governance models could draw from other small British Overseas Territories like Pitcairn and Ascension Island.
In November 2016, the United Kingdom restated it would not permit Chagossians to return to the islands.
In July 2021, the Chagos Refugees Group UK submitted a complaint to the Irish government against domain-name speculators Paul Kane and Ethos Capital subsidiary Afilias, seeking repatriation of the .io ("Indian Ocean") country-code top-level domain and payment of back royalties from the $7 million per year in revenue generated by the domain. While attempts to repatriate top-level domains are not uncommon, this one is notable in that it cites consumer and human rights violations of the OECD's 2011 Guidelines for Multinational Enterprises rather than multistakeholder representation under ICANN policy, and because the .IO domain has enjoyed commercial success, particularly among cryptocurrency companies, with more than 270,000 domains registered.
The Chagos had been administered from imperial offices in Mauritius since the 18th century when the French first named the islands. All of the islands forming part of the French colonial territory of Isle de France (as Mauritius was often then known) were ceded to the British in 1810 under the Act of Capitulation. In 1965, in planning before Mauritian independence, the UK split the archipelago from the territory of Mauritius to form the British Indian Ocean Territory, looking to provide the United States with an uninhabited island base, the country's main creditor following the turmoil of the Second World War.
United Nations' resolutions on self-determination deprecated the parcelling up of imperial territories before independence, without its endorsement and local support, mindful of the Partition of India which provided the strong governments sought by the separate factions but failed to ensure a relatively peaceful transfer of power in many places. Mauritius has repeatedly stated that the British claim that the Chagos Archipelago is one of its territories thwarted its claim to what would be widely considered part of the Mauritian colony and also breached UN resolutions. The UK has stated that the Chagos will be assigned to Mauritius once the islands are no longer required for defence purposes.
The island nation of Mauritius claims the Chagos Archipelago (which is coterminous with the BIOT), including Diego Garcia. Maldives states that the UK's claim to a 200 nautical mile Exclusive Economic Zone around the Chagos Archipelago is invalid as the islands are considered uninhabited. A subsidiary issue is the Mauritian opposition to the 1 April 2010 UK Government's declaration that the BIOT is a Marine Protected Area with fishing and extractive industry (including oil and gas exploration) prohibited.
On 16 November 2016, the UK Foreign Office maintained their ban on repatriation of the islands. In response to this decision, the Prime Minister of Mauritius expressed his country's plan to advance the sovereignty dispute to the International Court of Justice. The British Foreign Secretary Boris Johnson sought Indian assistance for resolving the dispute involving the UK, the US and Mauritius. India has maintained considerable influence in Mauritius through deep cultural and economic ties. India has maintained that the matter of whether or not to proceed with the UN General Assembly move is a decision for the Mauritian government to make.
On 22 June 2017, the UN General Assembly requested the International Court of Justice to give an advisory opinion on the separation of the Chagos Archipelago from Mauritius. On 25 February 2019, the International Court of Justice advised that in its opinion:
On 23 June 2017, the United Nations General Assembly (UNGA) voted in favour of referring the territorial dispute between Mauritius and the United Kingdom to the International Court of Justice (ICJ) in order to clarify the legal status of the Chagos Islands archipelago in the Indian Ocean. The motion was approved by a majority vote with 94 voting for and 15 against.
On 22 May 2019, the United Nations General Assembly debated and adopted a resolution that affirmed that the Chagos archipelago “forms an integral part of the territory of Mauritius.” The resolution demanded that the UK "withdraw its colonial administration ... unconditionally within a period of no more than six months." 116 states voted in favour of the resolution, 55 abstained and only 5 countries supported the United Kingdom. During the debate, the Mauritian Prime Minister, Sir Anerood Jugnauth, described the expulsion of Chagossians as "akin to a crime against humanity," while the United Kingdom continued to assert that it had no doubt about its sovereignty over the archipelago. The Maldives were one of the countries which supported the UK in the General Assembly vote. It stated that, if the Chagos Archipelago became inhabited, the Maldives claim to an extension of its Exclusive Economic Zone would be affected. The resolution's immediate consequence was that the UN and other international organisations became bound by UN law to support the decolonisation of the Chagos Islands.
On 25 February 2019, the International Court of Justice (ICJ) delivered an advisory opinion that placing the Archipelago under British administration in 1965 was not based upon the free expression of the inhabitants and that it thus advised that the United Kingdom should relinquish the archipelago, including the strategic United States military base, for the establishment of which approximately 1,500 inhabitants had been deported. The British government rejected any jurisdiction of the court to deliberate these matters.
The United Nations General Assembly (UNGA) voted in favour of setting a six-month deadline for the United Kingdom to withdraw from the Chagos Archipelago, which would then be reunified with Mauritius. The motion was approved by a majority vote with 116 voting for and 6 against. Fifty-six states, including France and Germany, abstained.
On 28 January 2021, the United Nation's International Tribunal for the Law of the Sea (ITLOS) confirmed the International Court of Justice ruling and ordered Britain to hand over the Chagos Archipelago to Mauritius. The ITLOS Special Chamber affirmed that: “it is inconceivable that the United Kingdom, whose administration over the Chagos Archipelago constitutes a wrongful act of a continuing character and thus must be brought to an end as rapidly as possible, and yet who has failed to do so, can have any legal interests in permanently disposing of maritime zones around the Chagos Archipelago by delimitation”.
On November 26, 2021, Mauritius amended its Criminal Code through the Criminal Code (Amendment) Act 2021 to introduce Section 76B, which criminalizes actions that misrepresent Mauritius' sovereignty over any part of its territory. The law applies to individuals acting under the authority, instructions, or financial support (direct or indirect) of a foreign state and imposes penalties of a fine or imprisonment of up to 10 years. Offenses include producing, distributing, or marketing coins, stamps, maps, or official documents that misrepresent Mauritius' sovereignty, as well as instructing others to do so. A "foreign state" under this provision refers to any country that an international court or tribunal has determined to have no valid claim over any part of Mauritius' territory.
On 14 February 2022, a delegation from Mauritius, including the Mauritian ambassador to the UN, raised the Mauritian flag on the Chagossian atoll of Peros Banhos. The move was done in the context of a scientific survey of Blenheim Reef but was regarded as a formal challenge to British sovereignty over Chagos.
On 3 November 2022, the British Foreign Secretary James Cleverly announced that the UK and Mauritius had decided to begin negotiations on sovereignty over the British Indian Ocean Territory, taking into account the recent international legal proceedings. Both states had agreed to ensure the continued operation of the joint UK/US military base on Diego Garcia.
Whereas these talks included the resettlement of expelled Chagossians, Cleverly's successor as British foreign secretary, David Cameron, later ruled out a return of the islanders.
On 3 October 2024, the UK Government made a joint statement with the Mauritian government that they had negotiated for the sovereignty of the Chagos Islands following two years of negotiation whilst still enabling the running of the American military base on Diego Garcia, thereby ruling out the right of return of the Chagossians to that specific island. The deal has come under criticism as Chagossians were not involved in the negotiations. On the same day, former Maldivian President Mohamed Nasheed stated that the decision to hand over the Chagos Islands to Mauritius, despite the Maldives' claims, was unacceptable. On 6 October 2024, the Democrats Party of the Maldives expressed concern that Maldives President Mohamed Muizzu’s administration had not been making efforts to assert the Maldives' claim over the Chagos Archipelago, as promised in the presidential pledge.
There has been a consistent theme of negotiations and decisions about the Chagos Islands being made without directly involving or consulting the Chagossian community. This exclusion from the sovereignty negotiations between the UK and Mauritius has fuelled opposition among Chagossians, who feel their voices have been deliberately ignored in determining the future of their homeland. They demand full inclusion in any discussions or treaties regarding the Chagos Islands.
The Chagossians have been engaged in numerous legal battles over their right to return and the sovereignty of the islands. Legal actions like those initiated by Bernadette Dugasse against the UK government for failing to include Chagossians in sovereignty talks further underscore their opposition to decisions made without their input. This reflects a broader struggle for recognition of their rights and sovereignty over their land.
Structures on the islands are located in the joint defence and Naval Support Facility Diego Garcia, although the Plantation house and other structures left behind by the Ilois are still standing, however left abandoned and decaying. Other uninhabited islands, especially in the Salomon Atoll, are common stopping points for long-distance yachtsmen travelling from Southeast Asia to the Red Sea or the coast of Africa, although a permit is required to visit the outer islands.
The islanders were known as the Ilois (a French Creole word for "islanders") and they numbered about 1,000. They were of mixed African, South Indian, Portuguese, English, French and Malay descent and lived very simple, spartan lives in their isolated archipelago working in the coconut and sugar plantations, or in the fishing and small textile industries. Few remains of their culture have been left, although their language is still spoken by some of their descendants in Mauritius.
The inhabitants of Chagos were speaking Chagossian Creole, also known as Ilois creole, a French Creole which has not been properly researched from the linguistic point of view.
The island names are a mixture of Dutch, French, English and Ilois Creole.
The Ilois who inhabited the islands were forcibly removed by the US and British governments during the late 1960s and early 1970s—effectively turning the islands into a military base. While a number of islanders had petitioned for the return of their former homes and their right to return has been recognised by the UN General Assembly, the International Court of Justice, and the International Tribunal for the Law of the Sea, the US and UK legal systems have refused to adhere to these decisions, leaving the Chagossians in exile.
Diego Garcia is currently the only inhabited island in the Chagos, all of which compose the British Indian Ocean Territory, usually abbreviated as "BIOT". The UK considers it an Overseas territory of the United Kingdom, and the Government of the BIOT consists of a Commissioner appointed by the King on the advice of the Foreign and Commonwealth Office. The Commissioner is assisted by an Administrator and small staff, and is based in London and resident in the Foreign and Commonwealth Office. This administration is represented in the Territory by the Officer commanding British Forces on Diego Garcia, the "Brit Rep". Laws and regulations are promulgated by the Commissioner and enforced in the BIOT by the British Representative.
There are no indigenous peoples living on the island, and the UK represents the Territory internationally. A local government as normally envisioned does not exist. Around 1,700 armed services personnel and 1,500 civilian contractors, mostly American, are stationed on Diego Garcia.
As of 2012, the islands have a transitory population of about 3,000 including 300 British government personnel, 2,700 United States Army, Navy and Air Force personnel.
The Catholics are pastorally served by the Roman Catholic Diocese of Port-Louis, which includes the BIOT.
The Chagos, together with the Maldives and Lakshadweep, forms the Maldives-Lakshadweep-Chagos Archipelago tropical moist forests terrestrial ecoregion. The islands and their surrounding waters are a vast oceanic Environment Preservation and Protection Zone (EPPZ) (Fisheries Conservation and Management Zone (FCMZ) of 544,000 square kilometres (210,000 sq mi)), an area twice the size of the UK's land surface.
The deep oceanic waters around the Chagos Islands, out to the 200 nautical mile limit, include an exceptional diversity of undersea geological features (such as 6000 m deep trenches, oceanic ridges, and sea mounts). These areas almost certainly harbour many undiscovered and specially adapted species. Although the deepwater habitats surrounding the islands have not been explored or mapped in any detail, work elsewhere in the world has shown that high physical diversity of the sea floor is closely linked to a high diversity of species.
The biodiversity of the Chagos archipelago and its surrounding waters is one of the main reasons it is so special. As of 2010, 76 species that call Chagos home were listed on the IUCN Red List of Threatened Species.
The reefs host at least 371 species of coral including the endemic brain coral Ctenella chagius. Historically, the coral cover was dense and healthy even in deep water on the steep outer reef slopes. Thick stands of branching staghorn coral (Acropora sp) previously protected the low-lying islands from wave erosion. Despite the loss of much of the coral in a bleaching event in 1998 the recovery in the Chagos was remarkable and overall coral cover increased year on year to 2014. High water temperatures, however, caused coral bleaching in both 2015 and 2016 which resulted in the death of more than two thirds of corals.
The reefs are also home to at least 784 species of fish that stay near to the shores of the islands including the endemic clownfish (Amphiprion chagosensis) and many of the larger wrasse and grouper that have already been lost from over-fishing in other reefs in the region.
As well as the healthy communities of reef fish there are significant populations of pelagic fish such as manta rays (Manta birostris), whale sharks, other sharks, and tuna. Shark numbers have dramatically declined as a result of illegal fishing boats that seek to remove their fins and also as accidental by-catch in the two tuna fisheries that used to operate seasonally in the Chagos.
Seventeen species of breeding seabird can be found nesting in huge colonies on many of the islands in the archipelago, and 10 of the islands have been designated Important Bird Areas by BirdLife International. This means that Chagos has the most diverse breeding seabird community in this tropical region. Of particular interest are the large colonies of sooty terns (Sterna fuscata), brown and lesser noddies (Anous stolidus and Anous tenuirostris), wedge-tailed shearwaters (Puffinus pacificus) and red-footed boobies (Sula sula). Land bird fauna is poor and consists of introduced species and recent natural colonisers. Red fody has been introduced and is now widespread.
Environments in the Chagos Archipelago provide rich biodiversity and support varieties of cetacean species, such as three populations of blue whales and toothed whales (sperm, pilot, orca, pseudo-orca, risso's and other dolphins such as spinners). Dugongs are now locally extinct but once thrived in the archipelago and Sea Cow Island was named after the presence of the species. Donkeys left behind when the Ilois were relocated also roam free.
The remote islands make perfect undisturbed sites for nests of green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles. The populations of both species in Chagos are of global significance given the critically endangered status of hawksbills and the endangered status of green turtles on the IUCN Red List. Chagos turtles had been heavily exploited for two centuries but they and their habitats are now well protected by the government of the British Indian Ocean Territory and are recovering well.
The coconut crab (Birgus latro) is the world's largest terrestrial arthropod, reaching more than a metre in leg span and 3.5–4 kilos in weight. As a juvenile it behaves like a hermit crab and uses empty coconut shells as protection, but as an adult this giant crab climbs trees and can crack through a coconut with its massive claws. Despite its wide global distribution, it is rare in most of the areas in which it is found. The coconut crabs on Chagos constitute one of the most undisturbed populations in the world. An important part of their biology is the long distances their young can travel as larvae. This means the Chagos coconut crabs are a vital source for replenishing other over-exploited populations in the Indian Ocean region.
113 species of insect have been recorded from the Chagos Islands.
The Chagos Islands were colonised by plants once there was sufficient soil to support them—probably less than 4,000 years. Seeds and spores arrived on the emerging islands by wind and sea and from passing seabirds. The native flora of the Chagos Islands is thought to consist of forty-one species of flowering plant and four ferns, as well as a wide variety of mosses, liverworts, fungi and cyanobacteria.
Today the status of the Chagos Islands’ native flora depends very much on past exploitation of particular islands. About 280 species of flowering plant and fern have now been recorded on the islands, but this increase reflects the introduction of non-native plants by humans, either accidentally or deliberately. As some of these non-native species have become invasive and pose a threat to the native ecosystems, plans are being developed to control them. On some islands native forests were felled to plant coconut palms for the production of copra oil. Other islands remain unspoiled and support a wide range of habitats, including unique Pisonia forests and large clumps of the gigantic fish poison tree (Barringtonia asiatica). Unspoiled islands provide us with the biological information that we need to re-establish the native plant communities on heavily altered islands. These efforts will ultimately help to improve the biodiversity of the Chagos Islands.
Successive UK governments, both Labour and Conservative, have supported environmental conservation of the Chagos. They have committed to treating the whole area as a World Heritage Site. In 2003 the UK government established an Environment (Protection and Preservation) Zone under Article 75 of the UN Convention on the Law of the Sea extending 200 nautical miles from the islands. On eastern Diego Garcia, the largest island of the Chagos and the site of a UK–US military facility, Britain has designated the very large lagoon and the eastern arm of the atoll and seaward reefs as a "wetland of international importance" under the Convention on Wetlands of International Importance (the Ramsar Convention).
On 1 April 2010 Britain announced the creation of the Chagos Marine Protected Area, the world's largest continuous marine protected reserve, with an area of 545,000 km (210,000 sq mi).
This followed an effort led by the Chagos Environment Network, a collaboration of nine leading conservation and scientific organisations seeking to protect the rich biodiversity of the Chagos Archipelago and its surrounding waters. The Chagos Environment Network cites several reasons for supporting a protected area.
The UK government opened a three-month public consultation, which ended after 5 March 2010, on conservation management of the Chagos Islands and its surrounding waters.
On 1 April 2010 the British government Cabinet established the Chagos Archipelago as the world's largest marine reserve. At 640,000 km it is larger than France or the US state of California. It doubled the total area of environmental no-take zones worldwide. The protection of the marine reserve will be guaranteed for the next five years thanks to the financial support of the Bertarelli Foundation. The setting up of the Marine Reserve would appear to be an attempt to prevent any repatriation by the inhabitants evicted in the 1960s and 1970s. Leaked US cables have shown the FCO suggesting to its US counterparts that setting up a protected no-take zone would make it "difficult, if not impossible" for the islanders to return. The reserve was then created in 2010.
On 18 March 2015 the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) that the UK had declared around the Chagos Archipelago in April 2010 violated international law. Anerood Jugnauth, Prime Minister of Mauritius, pointed out that it was the first time that the UK's conduct with regard to the Chagos Archipelago had been considered and condemned by any international court or tribunal. He qualified the ruling as an important milestone in the relentless struggle, at the political, diplomatic and other levels, of successive governments over the years for the effective exercise by Mauritius of its sovereignty over the Chagos Archipelago. The tribunal considered in detail the undertakings given by the United Kingdom to the Mauritian Ministers at the Lancaster House talks in September 1965. The UK had argued that those undertakings were not binding and had no status in international law. The Tribunal firmly rejected that argument, holding that the undertakings became a binding international agreement upon the independence of Mauritius and had bound the UK ever since. It found that the UK's commitments towards Mauritius in relation to fishing rights and oil and mineral rights in the Chagos Archipelago were legally binding. The Tribunal also found that the United Kingdom's undertaking to return the Chagos Archipelago to Mauritius when no longer needed for defence purposes was legally binding. This establishes that, in international law, Mauritius has real, firm and binding rights over the Chagos Archipelago and that the United Kingdom must respect those rights. The Tribunal went on to hold that the United Kingdom had not respected Mauritius’ binding legal rights over the Chagos Archipelago. It considered the events from February 2009 to April 2010, during which time the MPA proposal came into being and was then imposed on Mauritius.
According to United States diplomatic cables published by WikiLeaks, the UK and US wanted to safeguard the strategic value of the Chagos Islands.
WikiLeaks published a cable from the US embassy in London to Washington stating: