Post-1996 Scholarly Interpretations of theLegal Status of Threat of Force
Ariana N. SmithLAWYERS COMMITTEE ON NUCLEAR POLICY
December 2018

Post-1996 Scholarly Interpretations of the Legal Status of Threat of Force
Ariana N. Smith
International norms prohibiting the use of armed force pre-date the Charter of theUnited Nations (see: the Kellogg-Briand Pact1), but the Charter of the United Nations (“theCharter”) distinctly codified the prohibition of the use of force in Article 2(4) leaving only
two legal methods by which to pursue force.2 Concurrently addressed in the text—but
disproportionately ignored in legal analyses—is the additional prohibition of threats of force.
While both the use and threat of force are prohibited in parallel form in the Charter, manyscholars and practitioners disagree as to whether the lawfulness of threats of force isproperly interpreted as identical to the lawfulness of use of force. In considering threatsspecifically, identifying the threshold that distinguishes acceptable defensive military
preparedness from a readiness to exert illegal armed force in a particular situation can beconvoluted and often requires a heavy, contextual analysis. Nonetheless, the standard forthe legality or illegality of a threat of force—established in Article 2(4) of the Charter—
remains the same; it is the application of this standard that relies on context and theparticular facts of any conflict. As such, understanding the proper legal standard is essential.

1

General Treaty for the Renunciation of War as an Instrument of National Policy (August 27, 1928)

2

The Charter of the United Nations, art. 2, para. 4. (1945).
2

Threats of force carry particular weight when issued (or inferred) in reference to weaponsof mass destruction like nuclear warheads. In 1996, the International Court of Justice (ICJ)
issued an advisory opinion on the legality of nuclear weapons after the General Assembly
requested guidance.3 Twelve years later, though, ambiguity persists, nuclear deterrence
policies remain the status quo, and states continue to threaten nuclear destruction withvarying levels of credibility. Particularly as we move into a world where nuclear weapon
states are modernizing rather than disarming, and multi-polarity challenges the status quoof previous decades, it is important to thoughtfully consider an appropriate interpretation of
the legal prohibition of threats of force and its implications.
This paper will consider the legal status of the prohibition on threats of force asinterpreted by scholars and demonstrated through certain case studies. The first section will
identify and consider the relevant legal instruments to this analysis, as well as more generalpolicies at issue, like nuclear deterrence. The next section will consider several of the leading
academic voices on the legality of threats of force in international law. While many scholars
have analyzed the legality of use of force since the codification of the general prohibition in
the Charter, fewer have conducted in-depth analyses of the legality of threats. The third

3

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996 , 226 - 227.

See: https://www.icj-cij.org/files/case-related/95/095-19960708-ADV-01-00-EN.pdf
3section will consider a few instances of illegal threats highlighted by the authors, including
findings of a tribunal and independent fact-finding mission pertaining to specific conflicts.
Fourth, I will briefly analyze the current scholarship to identify the most persuasive
arguments. Finally, I will conclude with my view of the strongest interpretation of the legal
status of threat of force generally as well as in relation specifically to threats of nuclear
force. I will conclude that threats of force are illegal certainly when issued as a challenge tothe territorial integrity or political independence of a state, as expressly stated in theCharter, and also likely illegal in many scenarios beyond these two circumstances, so long as
the “envisaged use of weapons” would be contrary to humanitarian law.4 To that end, I will
specifically conclude that threats of nuclear force are always unlawful.
Relevant Legal Instruments and Institutions
The instruments and institutions that provide a foundation for understanding theprohibition on threats of force include the Charter of the United Nations—specifically
Articles 2(4) and 51, the International Court of Justice (ICJ)—in particular the Court’s 1996

Nuclear Weapons Advisory Opinion, the Rome Statute of the International Criminal Court(ICC) and its Kampala Amendments, the Nuclear Non-Proliferation Treaty (NPT), and the4

Legality of the Threat of Use of Nuclear Weapons Advisory Opinion , I.C.J. Reports 1996.
42017 Treaty on the Prohibition of Nuclear Weapons (TPNW). It is also helpful to understandpolicies of nuclear deterrence generally.
First, the Charter of the United Nations sets the legal foundation for the prohibitionon the threat of force. Held concurrently in the text with the prohibition on the use forforce, the legal status of the threat of force is often subsumed in the prohibition of use—
meaning many would consider that where use of force is illegal, so is the threat of the sameforce. The Charter’s prohibition lies in Article 2(4) and states:
All Members shall refrain in their international relations from the threat or use offorce against the territorial integrity or political independence of any state, or in any
other manner inconsistent with the purposes of the United Nations.5 6

While Article 2 does not make clear whether the proscribed threat or use of force is
exclusive to military action or also includes economic, political or other variations of force,read in the context of the Charter as a whole (“armed force shall not be used…”)7, mostscholars interpret Article 2 as referring to armed force. In the context of the Charter as

5

The Charter of the United Nations, art. 2, para. 4. (1945).

6

A. Randelzhofer, B. Simma, ed., The Charter of the United Nations. A Commentary, 200, vol. I(Oxford, OUP 2002).
7

The Charter of the United Nations, preamble (1945).
5whole, when interpreting the legality of threats of force specifically, it is important to notethat the threat of force is prohibited not only against the territorial integrity or politicalindependence of any state, but also prohibited in broader way—that is, when the threat
operates in any way inconsistent with the purposes of the UN. As such, threats of force may

still be unlawful even if the territorial integrity or political independence of a state is notthreatened.
The prohibition of use of force finds two explicit exceptions in the Charter: theSecurity Council’s authority under Article VII and Article 51 (self-defense). Similarly, scholars
cite both exceptions to the prohibition on threat of force as well, in particular Article 51.
Article 51 establishes the legal standard for self-defense, and reads:
Nothing in the present Charter shall impair the inherent right of individual orcollective self-defence if an armed attack occurs against a Member of the United
Nations, until the Security Council has taken measures necessary to maintaininternational peace and security.8

8

The Charter of the United Nations, art. 51 (1945).
6

Several of the authors below discuss when a threat of force (whether or not followedby actual use of force) may be lawful in self-defense and when such a threat on its own
constitutes illegal action. James Green and Francis Grimal, whose work is further discussed
below, look particularly closely at when a threat of force may qualify as an appropriate legal
strategy of self-defense.
The International Court of Justice (ICJ) is the primary judicial body of the UN. The ICJ
hears and decides cases between member-states and may also issue advisory opinions whenrequested. The advisory opinions serve an important purpose in interpreting internationallaw on the whole and identifying developing norms. The ICJ’s 1996 Nuclear Weapons

Advisory Opinion is of particular relevance to any discussion on threat of nuclear force.9
Scholars also refer to the Court’s 1986 Nicaragua opinion as well as the Corfu Channel
case—one the court’s earliest decisions—for guidance interpreting the prohibition of threatsof force in international law.10
In the ICJ’s 1996 Nuclear Weapons opinion, issued in response to a 1994 requestfrom the UN General Assembly, the Court concluded that while international law does not

9

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996, 226 - 227.

See: https://www.icj-cij.org/files/case-related/95/095-19960708-ADV-01-00-EN.pdf
10

Corfu Channel Case (United Kingdom v. Albania), I.C.J. Reports 1949; Nicaragua v. United States ofAmerica, I.C.J. Reports 1986.
7

specifically proscribe the threat or use of nuclear weapons, international law pertaining toforce—including humanitarian law—applies to nuclear weapons as it would to otherweaponry.11 The Court, though, largely abstained from issuing any clarifying guidance on thelegal status of nuclear weapons generally. While the Court found that threat or use of
nuclear weapon would “generally” be in conflict with international law, it would “notconclude definitively whether the threat or use of nuclear weapons would be lawful or
unlawful in an extreme circumstance of self-defense, in which the very survival of a State
would be at stake.”12 The language “the very survival of a State” raises more questions thanit offers answers regarding what circumstances threaten a state’s survival. The Court’s judges
were divided over this issue, and multiple judges issued separate opinions in addition to themain Advisory opinion. While the court abstained from declaring nuclear weapons or theirpossession inherently illegal or unlawfully threatening, the ICJ president at the time,
Mohammed Bedjaoui, said: “I cannot sufficiently emphasize that the Court’s inability to go
beyond this statement of the situation in no way can be interpreted to mean that it is11

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996 , p. 226,

257.
12

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996, p. 226,266.
8

leaving the door ajar to recognition of the legality of the threat or use of nuclear
weapons.”13
Next, the Rome Statute and its definition of the crime of aggression—codified in the
Kampala Amendments in 2010—are relevant when analyzing threats of force as well. The
Rome Statute is one of the primary instruments of international law to develop after theCharter. In 2010, the Kampala Amendments to the Rome Statute defined and codified
aggression; legal accountability for the international crime finally went into force in July
2018. The crime of aggression is committed by “the planning, preparation, initiation, or
execution, by a person in a position effectively to exercise control over or to direct thepolitical or military action of a State, of an act of aggression, which, by its character, gravity
and scale, constitutes a manifest violation of the Charter of the United Nations.”14 An act ofaggression is defined as “the use of armed force by a State against the sovereignty,
territorial integrity or political independence of another State, or in any other mannerinconsistent with the Charter of the United Nations.”15 Marco Roscini, discussed below, notesthat many state parties to the Rome Statute were reluctant to include any reference to

13

Sauer, Tom and Joelien Pretorius. “Nuclear weapons and the humanitarian approach” in Global

Change Peace & Security Sept. 2014.
14

UNGA, Rome Statute of the International Criminal Court (amended 2010), 17 July 1998, art. 8(1).

15

Id.
9

threats in the definition of the crime of aggression. Indeed, threats of force were explicitly
excluded when the statute was updated with a definition through the Kampala
Amendments16 The preambular paragraph of the Statute, though, does reference threats,
but exclusively by way of referring to the Statute’s foundation in the principles of the UN
Charter, including Article 2(4).17
While many of the preparatory meetings proposed—and rejected—drafts of adefinition that included threats of aggression; ultimately the definition that succeeded allows
us to properly interpret the Statute to criminalize only actual aggression. The Statute splits
aggression into stages, such as “planning and preparation”; however, if any of the earlier
stages, including planning and preparation do not evolve into armed force-aggression, it
would not constitute the crime. The scholars discussed below agree that the Statute does
not directly implicate interpretations of the threat of force, not even through planning andpreparation; as aggression is understood to require the actual use of force as detailed in thestatute.18 As any actual implementation of aggression would be unlawful, however, so
likewise would be any threat to engage in aggression.

16

Roscini, 268.

17

Rocsini 244; see also: Rome Statute, preamble.

18

UNGA, Rome Statute of the International Criminal Court (amended 2010), 17 July 1998, Art. 8(2)10The Treaty on the Non-Proliferation of Nuclear Weapons, or the Non-Proliferation
Treaty (NPT), is an effort to bridge the gap between the nuclear weapons states and nonnuclear weapons states while controlling the peaceful use of nuclear energy. While nottextually-specified among its preamble and eleven articles, the Treaty rests on threeoverarching themes. These substantive “pillars” are: 1) non-proliferation of nuclear weapons;2) disarmament; and 3) development of peaceful uses of nuclear energy.19 The disarmament
obligations of the nuclear weapon states are established in Article VI of the NPT, which
requires the pursuit of “good faith” negotiations to halt the nuclear arms race and nuclear
disarmament.20 The nuclear powers—the United States and Great Britain in particular—
advocate for a “step-by-step” approach to meeting their Article VI obligations for nuclear
disarmament, while the non-nuclear weapon states have repeatedly proposed, generally
unsuccessfully, resolutions that would end nuclear arms development entirely in order tobegin implementing Article VI’s further call for total disarmament.21
The 2017 Treaty on the Prohibition of Nuclear Weapons (TPNW) is the first legal
instrument that attempts to more fully enact the NPT’s disarmament provisions by calling

19

Id., 47.

20

UNGA, Treaty on the Non-Proliferation of Nuclear Weapons, art. VI (1970).

21

Burns, Richard. The Challenges of Nuclear Non-Proliferation (London: Rowman & Littlefield, 2015),

59.
11

for a complete prohibition on nuclear weapons—their possession, development, and, ofcourse, use. The preamble of the Treaty recalls that:
In accordance with the Charter of the United Nations, States must refrain in
their international relations from the threat or use of force against…any
State…and that the establishment and maintenance of international peace andsecurity are to be promoted with the least diversion for armaments of theworld’s human and economic resources”22 (emphasis added).

The text of the TPNW includes crucial language to proscribe threats of nuclear force
specifically, justifying its proscription with the basic tenets of international humanitarian law.
While it is unlikely that the nuclear weapon states will sign on to the treaty in theforeseeable future, the adoption of the TPNW by 122 UN member-states in July 2017solidifies the existing prohibitory norm against threats of nuclear force. The TPNW, though,will not be a binding instrument until it enters into force upon its 50 required ratifications.
Even then, the treaty will only bind those member-states who have ratified it. Its entry into

22

Treaty on the Prohibition of Nuclear Weapons, preamble (2017).
12

force, nonetheless, will reinforce the norms against the use and threat of use of nuclear
force.
In line with the humanitarian principles that provide the foundation for the TPNW,
the UN Human Rights Committee recently adopted a new general comment on the right tolife. The comment specifically refers to the threat or use of nuclear weapons, among otherweapons of mass destruction, as incompatible with respect for the right to life and statesthat such threat or use is likely criminal under international law, as nuclear weapons by theirnature are “indiscriminate in effect and are of a nature to cause destruction of human life ona catastrophic scale.”23 While nuclear weapons still number close to fifteen thousand today
and several countries maintain policies of nuclear deterrence, relying heavily on theircontinued weaponization, the TPNW along with the UNHRC’s newly-revised statedunderstanding of the right to life work in tandem to reinforce the norm against nuclear
weapons, including the threat of their use.
Finally, the nuclear powers have stalwartly implemented policies of nuclear
deterrence for decades, illustrated through positions like mutually-assured destruction(MAD) that promise nuclear retaliation upon attack. While MAD was a hallmark of the Cold23

UN Human Rights Committee, General Comment No. 36 on article 6 of the International Covenant

on Civil and Political Rights, on the right to life. para. 66 (2018).
13

War and the height of the nuclear arms race, deterrence policies remain the standard
among nuclear weapon states today. Deterrence refers generally to the policy ofmaintaining a nuclear arsenal that a state intends to use if subject to a nuclear or even a
conventional attack.24 The rationale of deterrence policies is that if a state is prepared tolaunch nuclear weapons, potential enemy states will refrain from attacking or infringing on
the nuclear weapon-possessing states’ sovereignty to avoid retaliation. In 1996, the ICJ
abstained from making any notable remarks on the legality of policies of deterrence, statingthat while the readiness and intention to use nuclear weapons must be “credible” to beeffective, whether that threat would be illegal per Article 2(4) depends on how the actualuse of the implied or threatened force would be implemented.25 While the ICJ explicitly said
in its Nuclear Weapons opinion that they could not decide the legality of deterrence, theCourt noted a growing movement in favor of nuclear-free zones and disarmament
generally.26 While the nuclear weapon states in particular tend to argue that deterrence
policies effectively serve their named purpose, the growing international consensus outside

24

Drummond, Brian, “Is the United Kingdom Nuclear Deterrence Policy Unlawful,” New Zealand

Yearbook of International Law 109, vol. 11 (2013).
25

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996 , p. 226,

246-247.
26

Id., 255.
14

the nuclear powers is that deterrence is insufficient to prevent the use of nuclear weapons;
many states and disarmament advocates believe that the only way to ensure against a
nuclear attack or accident is to proscribe the possession of weapons entirely.27 Under aregime where nuclear weapons are peremptorily prohibited, possession or development of
weapons is more likely to constitute a threat than it is today.
Literature Review
In recent decades, several scholars have considered the legality of threats of force as
distinct from use, and several lines of legal reasoning have developed as a result. Somescholars and practitioners view threats in the international context as wholly unlawful savefor the two explicit exceptions in the Charter. Marco Roscini and Nikolas Stürchler, discussed
below, tend to fall into this category. Others argue that threats of force actually hold an
important place in international relations and can serve the beneficial purpose of preserving
peace and preventing war, as seen in Romana Sadurska’s arguments. These voices argue
that under slightly more expansive circumstances, threats should be legal, in part because
they are already condoned and usefully so. While Sadurksa published her analysis of thelegal status of threats of force years before the ICJ’s Nuclear Advisory opinion,

27

Vail, Christopher. “The Legality of Nuclear Weapons for Use and Deterrence,” 48 Geo. J. Int’l L. 839

at 864. (2017).
15

contemporary voices continue to promulgate her thesis. Additional voices, such as Dino
Kritsiotis, consider threats between states, whether or not ultimately illegal, as somewhat
inevitable and find that evolving legal interpretations should be tailored to account for this.
Central to this discussion is, of course, defining what actually constitutes a threat offorce. Among the literature below, each author establishes their own working definition
Commonalities among definitions include that a threat comprises an express or implied
credible assertion, from one state to a target state, of readiness to engage in force, should
the targeted state trigger a particular condition, usually within the context of a dispute.
Romana Sadurksa writes that it is important for scholars to distinguish between theinternational principle prohibiting the threat of force and the actual practice that occurs
more ambiguously and pragmatically by states.28 The types of threats that would violate
Article 2(4) of the UN Charter, according to the Charter’s own rationale, are only those that
produce the same or similar results to the illegal actual use of force. This means that unlessa threat of force leads in and of itself to the jeopardizing of peace or “massive violations ofhuman rights,” it is likely permissible, according to Sadurska.29 This is an expansive reading

28

Sadurska, Romana. “Threats of Force,” The American Journal of International Law, vol. 82, no. 2(April 1988), 239-268.
29

Sadurska, 250.
16

of the Charter’s text and allows extraordinary room for argument that a certain threat is
lawful, so long as it lessens the likelihood of conflict—a notoriously difficult proposition toprove. Sadurska, though, finds that if the Charter prohibits the threat of force in order toprevent international instability and human rights abuses, then so long as a threat does not
violate this underlying purpose of the Charter, a state may issue a threat and still remain incompliance with the general prohibition.30 Her permissive definition claims that many threatsof force actually function as a better alternative to the actual use of force and have
diplomatic value that should be—and has been—supported by the international
community.31
Sadurska claims that states consider not only Article 2(4) in determining the legalityof a threat but go beyond the text and also consider threats lawful if they 1) are made toprotect the security of the state, providing that the internal self-determination of the target
is not violated; 2) are made to vindicate a denied right of a state; or 3) are “prudent,”balancing individual and community values.32 Sadurska references specific instances of each

30

Id.

31

Id.

32

Sadurksa, 262-65.
17

of these lawful expressions of threat through the Cuban Missile Crisis, the Falklands War,and the Corfu Channel case.33
Sadurska claims that the legal analysis of a threat of force would only equate to theanalysis of actual use of force when they produce comparable results—and a threat will
rarely have the same destructive results as the use of force, she says.34 She cites policies ofnuclear deterrence as compatible with UN purposes to the extent that they discourage
aggression.35 Ultimately, Article 2(4)’s black letter law cannot exclusively define the legal
bounds of threats of force, and any actions that further peace and stability “deserve legal
blessing” says Sadurska.36 Sadurska regards threats—at least under some circumstances—as
not only inevitable, but as a desirable tool of international relations. While some scholars
dismissed Sadurska’s argument that threats can often promote security and peace after the
1996 ICJ Nuclear Advisory opinion, in which the court chose not to adopt such an expansive
view, many others continue to trace her logic and apply her calculus of threat utility today.
Marco Roscini, on the other hand, finds that the ICJ’s Nuclear Advisory opinion
largely upended Sadurska’s theories that prohibitions on the threat of force are and should

33

Id., 254-263

34

Sadurska, 250.

35

Sadurska, 247-50.

36

Id., 266-68.
18

be considered distinct from use of force. Roscini finds the ICJ’s Nuclear opinion to clearlystate that if a threat of force is to be lawful, it must be a threat of force that, if carried out,
would be in full conformity with the Charter.37 Whether possessing nuclear weapons ormaintaining a policy of deterrence equates to a threat depends upon whether theenvisioned use of force would violate the Charter (i.e. if the force would be directed against
the territorial integrity or political independence of the State, against the purposes of theUN, or, if intended as a defense, if the use of force in defense would violate the principles ofnecessity and proportionality).38 Roscini views Sadurska’s utilitarian analysis ascounterproductive, claiming that interpretations like hers, and states that likewise support
the use of threats of force as a tool of de-escalation, “prevent the prohibition of the threatof force from being qualified as a peremptory norm of general international law.”39
Roscini defines unlawful threats as “explicit or implicit promise[s] of a future andunlawful use of armed force against another state, the realization of which depends on thethreatener’s will.”40 He claims that even if threats can contribute to international order or

37

Roscini, Marco “Threats of Armed Force and Contemporary International Law,” Netherlands

International Law Review 229, 255, vol. 54, 2007 (revised 2009).
38

Id., 255.

39

Id., 256.

40

Roscini, 256.
19

equilibrium, that does not unequivocally mean they are not also unlawful.41 In particular,
Roscini is concerned with the snowball effect of threats that can lead to armed conflict. Sucha scenario is exemplified in the Russo-Georgian War of 2008, discussed in the case study
section below. Roscini argues that there are degrees of threat, just as there are degrees offorce (the strongest being aggression). It follows, he says, that a prohibition of threats ofaggression at least logically holds as a peremptory norm, just as the use of force
constituting aggression does.42 On the whole, Roscini subscribes to the view that Article 2(4)does reflect the customary international law principle that threats of force are prohibitedalong the same lines as use of force, even though this prohibition is not jus cogens. The
prohibition on threats of aggression specifically, though, does represent a jus cogens norm.
As one of the two Charter-recognized exceptions to the prohibition of threat or use
of force, self-defense offers an interesting opportunity to analyze how threats of force may
be interpreted differently from use of force. James Green and Francis Grimal analyze theconceptual possibility—and the desirability—of threats of force made in self-defense.43 Theyfind that threats of force for the purpose of self-defense are both logically possible and in

41

Id., 254.

42

Id., 257.

43

Green, James A. and Francis Grimal, “The Threat of Force as an Action in Self-Defense underInternational Law,” Vanderbilt Journal of Transnational Law, vol. 44:285 (2011).
20

some cases appropriate policy. In harmony with Sadurksa’s reasoning, the authorsemphasize that defensive threats can uphold and promote the foundational principles of
Article 2(4) and the Charter as a whole as a non-forcible alternative to military action.44
Green and Grimal acknowledge, though, that there are inherent difficulties in determining
what behavior constitutes a lawful (non-forcible alternative to force) versus unlawful
defensive threat. Throughout their analysis, Green and Grimal analogize threats of defensive
force to actual defensive force and find that, as a starting point, threats of force mustcomply with the requirements of actual force (similarly to Rocini).45 They, like Roscini, basethis starting point on both Article 2(4) and the ICJ Nuclear Advisory opinion. Direct
application of the ICJ’s opinion, though, could lead to “absurd results” and counterintuitive
outcomes, Green and Grimal say, because of the “inherent consequential difference between
threatened and actual force.”46
Green and Grimal examine the legal status of threat of force in six hypotheticalscenarios, when a threat is made in response to: 1) a grave use of force (an armed attack);
2) a “less grave” use of force; 3) a threat of imminent grave force; 4) a threat of imminent

44

Green and Grimal, 239.

45

Green and Grimal, 295.

46

Id., 327.
21

“less grave” force; 5) a threat of non-imminent grave force; 6) a threat of non-imminent “lessgrave force.47 The authors conclude that a defensive threat would be lawful if made in
response to the first three scenarios. They also argue that the fourth action—a threat in
response to another’s threat of imminent less grave (i.e. something less than armed force)
force—may sometimes justify use of defensive threats as well, so long as the defensive
threat used is purely a deterrent would not escalate to actual use of force.48 The authors
offer the example of South Korea issuing a counter-threat against North Korea in 2010
following North Korea’s bombardment of Yeonpyeong Island. The South Korean threat wasissued in response to North Korea’s persistent threat of imminent “less grave” force and wasissued with a defensive posture—only if North Korea provoked again did South Korea
threaten to attack. The threat by South Korea was only intended to come to fruition if North
Korea provoked again (even if North Korea’s threatened action did not necessarily envision
actual “armed force”—hence “less grave” force).49 Finally, according to Green and Grimal,

47

Green and Grimal, 313.

48

Id., 318.

49

Green and Grimal, 318.
22

defensive threats in response to any non-imminent threats of force would be unlawful(scenarios five and six).50
Threats of force made in self-defense should also meet the criteria of necessity andproportionality, Green and Grimal say. These requirements must be considered more flexibly
than they would be for actual force used in self-defense, though. Necessity, the authors
posit, turns on the “acceptability” of the threat according to other states, including whether
the defensive threat is perceived as meeting a genuine defensive need.51 Proportionality
should be considered, they say, based on what is minimally required to effectively deter anaggressor—not based on the scale of the future force threatened.52 “Projected
proportionality” (what the ICJ in the Nuclear Weapons opinion supports) in contrast requires“impossible” calculations at a point before states have used force, say Green and Grimal.53
The authors pull from an example that originates with Sadurska and argue that a threat ofnuclear force may be lawful even if the use of force would not be proportional (as it could
not be), so long as the nuclear threat was considered the “only reasonable means” to deter

50

Id., 320.

51

Id., 323.

52

Green and Grimal, 324.

53

Id.
23

an aggressor state that had launched an attack—even a conventional attack.54 Sadurska—
and Grimal and Green—improperly fail to account for the indiscriminately lethal implicationsof threatening nuclear force by advancing this interpretation of proportionality, which
completely disregards humanitarian law as well as the ICJ and the Charter’s roles in
upholding the principles of humanitarian law.
Grimal, in a separate book, offers his interpretation of threats in the nuclear context
specifically.55 He starts by identifying the general legal test for a threat of force’s legality as
beginning with a presumption of illegality. “A state threatening another starts in a positionof unlawfulness and has to justify the lawfulness of its threats by arguing that actual force
would be lawful.”56 The threat will only be lawful if the envisioned use of force would itself
be in conformity with the Charter; in this case, Grimal determines that the threat is a“legitimate warning and reminder”—and so does not violate the Charter and is notunlawful.57 International instruments do not provide an affirmative basis for legal threats,
generally speaking. Grimal refers to the view of international lawyer Ian Brownlie that one

54

Id.

55

Grimal, Francis. Threats of Force: International Law and Strategy. Routledge, Taylor & Francis Group,

2014.
56

Grimal, 37.

57

Id.
24

can only determine the legality of a threat of force retroactively or through hypotheticalanalysis—if the use of force threatened would be in conformity with the Charter, then thethreat of such force would likewise be lawful under the Charter. Alternatively, if there is no
justification for the use of force threatened, “the threat itself is illegal.”58
In applying this framework to nuclear threats in particular, Grimal considers threequestions: 1) what is the point at which a state’s nuclear program may constitute a threat offorce?; 2) could withdrawal from the NPT constitute a threat of force?; and 3) could being a
non-signatory to the NPT alone constitute a threat of force? Grimal concludes thatdevelopment of a nuclear weapon program by a non-nuclear weapon state could neverconstitute a breach of Article 2(4), nor could possession of a nuclear weapon. 59
On the second question, Grimal interestingly first proposes that withdrawal form the
NPT may constitute a threat of force. While it does not form a prima facie threat, he relies
on an argument, again first posited by Sadurska, that even signing a treaty may constitute a
threat (i.e., if a state becomes a party to a treaty like the Warsaw Pact, a neighboring state
may “feel threatened” if it was opposed to communism).60 If signing a treaty can be a threat,

58

Grimal, 38. citing to Ian Brownlie, International Law and the Use of Force by States, 364 (1963).

59

Grimal, 121.

60

Grimal, 131.
25

so can withdrawal potentially, Grimal says, offering the example of North Korea’s withdrawal
from the NPT. Ultimately, whether a withdrawal is a threat depends on which state iswithdrawing and the context of the decision, Grimal says. He clarifies, though, that even if
other states “feel threatened,” withdrawal is, ultimately, not a threat of force per se. Further,while developing nuclear weapons may constitute a threat, it does not constitute an

unlawful threat.61
Grimal recognizes, though, the severe implications of threatening use of nuclear
weapons above and beyond conventional weapons. “It is still arguable that any violation of
the NPT could still constitute a threat of force given the nature and purpose of a nuclear

weapon” (emphasis added).62 Grimal here, acknowledges the inherent risks of threatening
nuclear force, even if such threat was never intended to result in actual use of force. A
breach of the NPT that is “serious and persistent”—qualifiers that are unsettled anddebatable, Grimal admits—is much more likely to constitute a threat of force.63 Ultimately,
Grimal is unsatisfied with the lack of precision offered in Article 2(4) for determining when61

Id.,132.

62

Grimal, 132.

63

Id.
26

an illegal threat of force has occurred, but finds that when nuclear weapons are at issue, any
threat is more likely than not unlawful.
Dino Kritsiotis, Professor of Law at the University of Nottingham, analyzes threats offorce since the Cold War and uses several case study examples to explore the effect of
threats of force since the 1990s on international politics.64 He begins with the admission thatthe legal background prohibiting threats of force is often contrasted by accepted statepractice. Kritsiotis cites to Judge Bruno Simma saying that effectiveness of the Charter interms of threat or use of force has reached a “breaking-point,” as illustrated by theprevalence of force and threats of force today, despite the prohibition.65 States seems toaccept threats as positive contributions to international political life, despite their black-letter
prohibition, to the extent that they prevent actual force. Kritsiotis focuses in particular on
threats of force in the context of “unresolved” international crises, for example, Iraq and the
U.S. in the 1990s, Iran and the U.S. throughout the Bush and Obama administrations, andalso the Corfu Channel case.66

64

Kritsiotis, Dino, “Close Encounters of a Sovereign Kind,” European Journal of International Law 299,

vol. 20, no. 2 (2009).
65

Kritsiotis, 300.

66

Id., 303.
27

Kritsiotis acknowledges that the legal standard from the Charter and the ICJ’s 1996

Advisory opinion is that where the envisioned force would be unlawful, the threat of suchforce would be likewise prohibited. He affirms the Court’s finding that not all threats offorce are unlawful per se—the clearly unlawful threats are those that threaten to secure
territory from another State or aim to cause another State to follow or not to follow certain
political or economic paths (“territorial integrity and political independence”). One must
consider each case of a signaled intention to use force separately, in its context, todetermine whether there is an unlawful threat. Kritsiotis also cites to Oscar Schachter andsays that Article 2(4) has not often been invoked as “clearly” prohibiting implied threats, likethe deployment of military forces or missiles.67 Again, context is key—blanket prohibitions
on threat are very narrow according to Kritsiotis. Evaluating the circumstances of any alleged
threat of force, case-by-case, including state reactions, is necessary to determine theirlegality, he claims. Kritsiotis recognizes that there is often no means of telling whether athreat of force will become actual force, but even so agrees with Sadurska that states have

67

Kritsiotis, 306.
28

in some instances seemingly recognized threats of force as not only tolerable, but virtuousalternatives to actual force68
Finally, in one of the more comprehensive tomes considering the legality of threat offorce, Nikolas Stürchler systematically analyzes theoretical conceptions of threats alongside
in-depth case studies demonstrating lawful and unlawful threats.69 Stürchler pushes backagainst the argument that state silence in reaction to possible Charter violations of theprohibition of threat of force equates to tacit approval, countering Kritsiotis and Sadurska
among others.70 He furthermore notes that dissenting state voices have grown in volume
and number, in particular with the growth of the Non-Aligned Movement (NAM).71 Stürchler
approaches the legality of threats from a two-pronged approach instead, considering firstwhere the violation threshold of Article 2(4) lies, and second, exploring under whatcircumstances, once the threshold has been passed, there might be a legal justification forviolation of the prohibition.72

68

Id. 308-309.

69

Stürchler, Nikolas, The Threat of Force in International Law. Cambridge University Press. 2007.

70

Stürchler, 257-258.

71

Sturchler, 257 (footnote 10).

72

Stürchler, 258.
29

First in his analysis is the threshold of violation. When is a threat of force unlawful
per the Charter? Stürchler finds that the primary test for a Charter-violating threat must
consider whether a state credibly communicates its readiness to use force in a particular
dispute.73 A threat is credible when it appears rational to implement it, when there is asufficiently serious commitment to run the risk of an armed encounter, he argues. This isabout calculated expectation—one does not need certainty as to whether force will be
carried out nor does one need specific demands or tight deadlines imposed by thethreatening country.74 There are two ways a government can render its threats credible,
Stürchler says: the state can openly commit to carrying out a threat to a domestic audience,increasing the political costs of a bluff, or it may declare to other governments its
willingness to use force, putting its international reputation on the line.75 While open andexplicit intent to use force may constitute a credible threat, inflammatory speeches are likely
not enough to fulfill the specific-language requirement of a credible threat, Stürchler says.76
Legally, the issue with relying on the credibility of a threat in determining whether itis lawful is that credibility is subjective. For example, many took President Trump very

73

Id., 259.

74

Id.

75

Stürchler, 260.

76

Id.
30

seriously when he threatened the total destruction of North Korea in his speech at theUnited Nations General Assembly in September 2017. While this is certainly an inflammatory
speech (which Stürchler would likely classify as not-credible), it also very likely did constitutea serious and illegal threat of force. The indiscriminate severity of nuclear force in particularmakes threats of that kind inherently more dangerous regardless of variations in credibility.
Finally, according to Stürchler, actual use of force may sometimes constitute a threat, too.77
Scholars continue to discuss whether measures of “coercive diplomacy,” including microlevel or limited uses of force (i.e. border clashes, retaliatory strikes, or naval blockades)
constitute actual or threatened force or whether they violate the Articles 2(4) or 51 of theCharter at all.78
Stürchler also considers the point at which, if any, amassing armaments or
militarizing might constitute a breach of Article 2(4). He points out that a defiance todisarm, if anything, is more likely to constitute a threat to the peace under Chapter VII thana violation of Article 2(4).79 History has also proven quite permissive of arms building andmilitarizing as sovereign acts. In the absence of a specific treaty obligation, he finds that77

Stürchler, 262

78

Id.

79

Stürchler, 263.
31

states likely retain the right to acquire weapons, including nuclear, in whatever quantity.80
Notably, nuclear weapon states party to the NPT have an obligation to disarm under Article
VI—and non-nuclear weapon states have an obligation not to develop weapons—however
the acquisition of these weapons does not constitute a threat alone, Stürchler says.81 Afterall, states party to the NPT, as any treaty, are free to withdraw; treaty obligations alone
cannot constitute a peremptory norm establishing the building of arms as a threat inviolation of Article 2(4), he says.
On the second prong, Stürchler considers the two main exceptions to the prohibitionof use of force as applied to the prohibition of threat of force: self-defense under Article 51
and Security Council authorization under Chapter VII. 82 He focuses on self-defense. Stürchler
identifies the clearest iteration of a lawful threat in self-defense as one issued in response to
an armed attack.83 The more nuanced question, he says, is whether states may reciprocate athreat lawfully when there has been no armed attack. States consistently consider a few
characteristics of the conflict at-issue when deciding whether issuing a threat is more likely
to assuage rather than exacerbate the conflict. In these scenarios, states are concerned

80Id., citing to the ICJ’s Nuclear Weapons opinion.

81

Stürchler, 263.

82

Id., 265.

83

Stürchler, 265.
32

about the “dynamics of escalation” as well as the possibility that a threat will offer anaggressor state the “pretext for military retaliation.”84
Finally, recognizing that many argue that the post-9/11 world shifted how threats arelegally interpreted, Stürchler addresses the myth of the threat-permissive 21st century, noting
in particular the heavy criticism of the U.S.-UK invasion of Iraq in 2003. Ultimately, there is
not a convincing record showing that the law governing threats of force was substantiallyrevised at all, he says.85
Case Studies and Institutional Findings from the Literature
While states regularly invoke the prohibition on use of force, and often do so bycoupling the prohibition of threat and use of force, “the threat of force has found little
articulation in state practice,” assert Green and Grimal.86 Stürchler, though, in reviewing
Kritsiotis’s article, refers to two recent iterations of threats of force that were ultimately
classified as unlawful.87 The first: a 2007 arbitration tribunal under the UN Convention on the

84

Id., 266.

85

Id., 271-72.

86

Green and Grimal, 286.

87

Stürchler, Nikolas. “Law’s Labours Lost? Comment on Dino Kritsiotis, Close Encounters of a

Sovereign Kind.” Blog of the European Journal of International Law. 25 Mar. 2010.
https://www.ejiltalk.org/laws-labours-lost-comment-on-dino-kritsiotis-close-encounters-of-asovereign-kind/.
33

Law of the Sea that determined that the Suriname Navy engaged in prohibited threats offorce against Guyanese oil ships.88 Stürchler secondly references the 2008 fact-finding
mission established by the Council of the European Union that determined both Russia andGeorgia had issued unlawful threats of force prior to the 2008 Russo-Georgian War.89
In 2007, the Suriname navy forcibly evicted personnel from an oilrig that Guyana hadallowed into the waters. Suriname and Guyana disputed ownership over that section of thesea, and Guyana alleged that Suriname engaged in both use of force against certain of its
licensed ships and threats of force against others. The arbitration tribunal analyzing theincident between Suriname and Guyana made its determinations after taking testimony fromseveral actors involved in the communication between the Suriname and Guyanese ships.90
While Suriname characterized their actions as intended only to achieve legitimate objectives,
the tribunal found that Suriname did engage in unlawful threats of force against the
Guyanese-associated ships. The tribunal agreed that even though Guyana could not have
known specifics about what “consequences” they might face—based on Suriname’s limited

88

Id.

89

Stürchler, Nikolas. “Law’s Labours Lost?”

90“Reports of International Abritral Awards regarding the delimitation of the maritime boundary

between Guyana and Suriname,” (Sept. 2007), 121. See: http://legal.un.org/riaa/cases/vol_XXX/1144.pdf
34

communication—for refusing Suriname’s orders to leave the sea, the threat was still credible
and in contradiction to Suriname’s obligations to engage in peaceful negotiation where
possible; as such, the threats of force issued by Suriname were deemed unlawful.91 92
The fact-finding mission of the Georgia-Russia conflict maintained that the mostimportant element in interpreting whether an iteration of state practice is a threat iscredibility.93 “A threat is credible when it appears rational that it may be implemented, when
there is a sufficient commitment to run the risk of armed encounter.”94 Credibility does not
require certainty as to whether force will be used, what conditions will trigger force, orwhether the threatened force is imminent, the findings stated.95 There need not be specificdemands or a deadline. “All that matters is that the use of force is sufficiently alluded to andthat it is made clear that it may be put to use.”96 Credibility is best understood in the91“Reports of International Abritral Awards regarding the delimitation of the maritime boundary

between Guyana and Suriname,” (Sept. 2007), 123. Note: the report also cites to the ICJ’s Nuclear

Weapons and Nicaragua opinions.
92

Id., 126-27.

93

Independent International Fact-Finding Mission on the Conflict in Georgia. Vol. II, Ch. 6: Use ofForce, 232. See: http://www.mpil.de/files/pdf4/IIFFMCG_Volume_II1.pdf.
94

Id., 232.

95

Independent International Fact-Finding Mission on the Conflict in Georgia. Vol. II, Ch. 6: Use ofForce, 232.
96

Id., 233.
35

context of an existing dispute.97 The fact-finding mission here found that Georgia issued
credible—and illicit—threats by engaging in air surveillance over the Abkhaz conflict zone,
participating exchanges of fire, and engaging in “comprehensive” military build-up, including
acquiring new weapons, with the assistance of a third-party state (the United States).98 The
fact-finders analyzed these actions in the context of Georgian behavior historically, findingthat because Georgia tended to “aggravate, rather than alleviate” tensions, Georgia’s
actions—considered under the totality of the circumstances—constituted threats of force.99
Notably, the report emphasized that even though Georgia may not have been able tosubstantially harm Russian integrity through force, their readiness to use force, signaled
through their actions, still constituted a credible and unlawful threat.100
The mission likewise found that the Russian Federation also consistently issued
credible and unlawful threats that contributed to the mounting tensions between the twostates. Russia’s actions that summed to a threat of force targeting Georgia included: warningthat Georgian NATO membership would result in the loss of territories and theestablishment of Russian military bases; another warning that Moscow would engage in

97

Id., 232.

98

Id., 233.

99

Id.

100

Independent International Fact-Finding Mission on the Conflict in Georgia. Vol. II, Ch. 6, 232.
36

force if Georgia initiated a conflict with Abkhazia and South Ossetia; Russia’s flying of
warplanes over Abkhazia and South Ossetia; Russia’s mobilization of troops to Abkhazia; andfinally, the Russian troops’ performance of a purportedly “regular” military exercise.101
The mission ultimately found that the threats issued from both sides leading to the
Russo-Georgian War did not fall under the Charter’s self-defense exception (neither were
they supported by the Security Council’s Article VII powers) and so were illegal.102 The report
goes on in great detail about the continuation and escalation of the conflict, indicating thatthe mutual threats helped heavily to foster a “climate of mistrust” that escalated into acrisis.103 Such escalation is one element that the prohibition of threats of force is meant todiscourage.
Critical Assessment
Often times, as in the Russo-Georgian fact-finding mission, the illegality of threat isbest discerned when it is either issued (like Russia’s warnings) or demonstrated (Georgia’s
air surveillance and arms acquiring; Russia’s military exercises) in the context of a dispute.
Standalone military exercises or troop mobilization, for example—and even warnings

101

Id., 234.

102

Id., 237.

103

Id., 238.
37

detached from any relevant dispute—likely do not amount to a threat of force. Preexisting
disputes tend to enable the states involved—and the rest of the international community—
to more accurately discern credibility and rationality, two factors that can prove quitedifficult to pin down, especially in independent instances of threat outside of any ongoing
dispute.
The scholars discussed above differ in the latitude they offer to states to issue what
they interpret to be legal threats of force that comport with the Charter and internationallaw on the whole. Sadurska, while attempting to take a pragmatic approach by recognizing
the inevitable continued existence of threats (some of which may support the purpose theCharter, she asserts), disregards the principle that some threats—even those consideredlegal and in legitimate self-defense—remain unlawful because the force envisioned within
the threat (regardless of its actual manifestation) would be to such a degree that it violatesinternational humanitarian law.104 The overarching theme of Sadurska’s argument seems torest, properly, on an understanding of one of the main purposes of the UN: maintaining
peace; however, she stretches this understanding to allege there is a wider legal margin of104

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996 , 257.
38

threat-making, effectively ignoring the relevant texts proscribing threats of force and thesubsequent interpretations of this proscription by the ICJ.
Generally, the largest challenge in interpreting the legal status of threats of force is
to balance the limited guidance provided by the legal instruments with the evidence ofoften seemingly unlawful state practice. Stürchler, though, points out that state practiceoften operates distinctly from the black letter law on threats of force, but contradictory statepractices (including state silence in the face of another state’s alleged violation of theprohibition on threat) does not negate the law. Silence in reaction to apparent violations of
the prohibition is often a result of innumerable political factors within and among the statesrather than a disregard for the legal prohibition of threats of force.
Roscini and Stürchler tend to identify the most persuasive threads of interpretation in
general by arguing for an interpretation of the proscription of threats parallel to theproscription of use of force with limited exceptions. Grimal furthermore provides a tangible
basis for exploring nuclear threats of force in particular, properly acknowledging that acts
such as withdrawal from the NPT or amassing arms, even in the face of treaty obligations,do not inherently violate the prohibition on threats found in Article 2(4). Practically, Grimal
offers a compellingly detailed breakdown of how to classify various threats of force and39their likelihood of legality when describing the six various scenarios in response to which astate may issue a threat. Grimal also, though, recognizes—in alignment with the recent UN
general comment on the right to life—that the inherently indiscriminate nature of nuclear
weapons makes any threat of their use particularly insidious and likely unlawful. In light of
the ICJ’s consistent evasion of requests seeking specific analysis of threats of nuclear force
or the implications of deterrence policies in light of the prohibition on threats, it is all themore important to maintain a realistic understanding of the immediate, catastrophic, andirreversible effects of nuclear weapons. Remembering Stürchler’s discussion pertaining to thethin line between threats that effectively stave off conflict and those that escalate into
further conflict, nuclear threats must be considered much more strictly. Threats of nuclear
force, under the Charter and the ICJ’s support for principles of proportionality andhumanitarian law in general, are always unlawful, as the risks of escalation associated with
nuclear threats are too high and too extreme.
Conclusion
Returning to the underlying goal of this article: what is the proper legal
interpretation of the prohibition against threats of force codified in the Charter of theUnited Nations? In analyzing the text of Article 2(4) along with post-Charter instruments and40interpretations, the baseline prohibition of threats of force, including nuclear force, isundeniably clear. The only threats of force that may have textual justification for legality arethose offered in narrow circumstances of self-defense and those authorized by the UN
Security Council. While threats of force issued in self-defense may sometimes be legal, even

if the threat is issued in response a prior threat or attack on a state’s territorial integrity orpolitical independence, the threat is still held to a standard by which it must comport withboth the general purposes of the United Nations, including the maintenance of peace, andinternational humanitarian law. If a threat otherwise in compliance with a state’s right toself-defense violates these additional principles, it is very likely unlawful. So, threats of force
are illegal certainly when issued as a challenge to the territorial integrity or politicalindependence of a state, as expressly stated in the Charter, and threats are also likely illegal
in many scenarios beyond these two circumstances, because any “envisaged use” of force
that would be contrary to humanitarian law is unlawful.105
To that end, threats of nuclear force are always unlawful. Furthermore, I would argue
that nuclear deterrence polices held closely by the nuclear weapons states in and ofthemselves constitute ongoing, unlawful threats of force. Recognizing the purposes of the105

Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996 , 257.
41

UN, the tenets of humanitarian law, and the proclamations (however limited) of the ICJ on
this point, there is no possibility of a legally-justified threat of nuclear force, regardless ofwhat may have provoked the threat. Proportionality, as recognized by the ICJ, among othercomponents of international law, simply does not leave room for lawful threats of nuclear
force.

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