The threat of force as an action in self-defense under international law.

Author:Green, James A.


Self-defense is a universally accepted exception to the prohibition of the use of force in international law, and it has been subjected to careful academic scrutiny. The prohibition of the threat of force, although equally important in terms of its normative status to the prohibition on use, has attracted far less academic commentary to date. This Article examines the relationship between the two prohibitions--of the use and threat of force--and considers the largely unexplored possibility of states utilizing a threat of force as a means of lawful defensive response: self-defense in the form of a threat. The status of this concept under international law is assessed, and the criteria that may regulate it are analyzed. This Article is based on an analogy between traditional "forcible" self-defense and the notion of threats made in self-defense. However, one cannot automatically apply the well-established rules of self-defense to a defensive threat, largely because of the practical differences between a threatened response and a response involving actual force.

TABLE OF CONTENTS I. INTRODUCTION II. THE THREAT OF FORCE IN INTERNATIONAL LAW A. The Source of the Prohibition of the Threat of Force B. The Jurisprudence of the ICJ and the "Coupling" of Use and Threat C. Typology of Threats of Force III. SELF-DEFENSE INVOLVING THE USE OF FORCE A. "Traditional" Self-Defense: The Use of Force in Response to the Use of Force B. Anticipatory and Preemptive Self-Defense: The Use of Force in Response to the Threat of Force IV. IS NON-FORCIBLE SELF-DEFENSE CONCEPTUALLY POSSIBLE? V. IS THE THREAT OF FORCE IN SELF-DEFENSE DESIRABLE? VI. THE CRITERIA FOR SELF-DEFENSE INVOLVING THE THREAT OF FORCE A. In Response to What? B. Necessity and Proportionality C. Note on Collective Self-Defense VII. CONCLUSION A bully is not reasonable.

He is persuaded only by threats.

--Marie de France, late twelfth century


    The prohibition of the threat of force stands directly alongside its loftier counterpart, the prohibition of the use of force, in Article 2(4) of the United Nations Charter. (1) Yet, although states continually reference the prohibition of the use of military force (even while breaking it), the scope and nature of the prohibition of the threat of force has found little articulation in state practice. This discrepancy is also apparent in the writings of scholars. As such, numerous questions remain unanswered with regard to the status of threats of force in international law. This Article considers one such issue: the relationship between the prohibition of the threat of force and the international law governing self-defense.

    In contrast to the legal status of threats of force generally, the lawfulness of forcible self-defense taken in response to a threat of force has been exhaustively, and exhaustingly, discussed in the academic literature. This debate over the lawfulness of "anticipatory" and "preemptive" self-defense has raged all the more fiercely since the atrocities of September 11, 2001, and the subsequent "war on terror." (2) However, the literature has left the inverted question, whether self-defense can be manifested by way of a threat of force, almost entirely unasked. (3) Therefore, it is not our intention to examine the question of whether military force taken in self-defense may be lawful in response to a threat. Instead, we ask whether a threat of force (a prima facie unlawful action under Article 2(4) (4)) can gain the status of lawfulness if taken as a defensive response, and, assuming that it can, we ask what criteria may be used to determine the lawfulness of such a defensive threat. This Article thus examines the legality of threats made in self-defense, which may also be referred to as "countervailing threats." (5)

    In 1996, as discussed in Part II, the International Court of Justice (ICJ) concluded that a threat of force is unlawful when the force threatened would itself be unlawful, and that, correspondingly, the threat to use force in a lawful manner is itself lawful. (6) If this conclusion is accepted, "not only is every threat illegal where force is illegal, but, obviously, any justification put forward for the use of force will work equally well for the threat of such force." (7) Self-defense is a universally accepted exception, enshrined in both Article 51 of the UN Charter and in customary international law, to the general prohibition of the use of force. (8) Therefore, countervailing threats of force may be lawful if the threatened force meets the criteria regulating the actual use of force in self-defense.

    Although a handful of other writers have also reached this conclusion, (9) none have taken the obvious next step and considered the criteria by which such a concept would be assessed. This Article aims to take that step, based on the core premise that defensive threats should be viewed as broadly analogous to "traditional" self-defense through the use of force. Having said this, it is not simply the case that the rules for the use of force in self-defense can be directly transposed to instances where a threat is employed. The use of force and the threat of force, while conceptually cut from the same legal cloth, are practically different actions with practically different consequences. (10) Therefore, the analogy to "traditional" self-defense is, on occasion, necessarily departed from or stretched.

    This basic assumption is nonetheless an important starting point because there is little legal guidance beyond it as to the criteria required to turn an unlawful threat of force into a lawful one. As previously noted, there is only a very small amount of literature on the notion of threats made in self-defense. Moreover, states simply do not make the explicit legal claim that the wrongfulness of any given threat is precluded because that threat constituted an act of self-defense. Analysis of state practice provides little to indicate how customary international law treats threats in self-defense, because states do not tend to respond to this issue in legal terms: "Practice does not seem sufficiently unambiguous to make unfailingly intelligible distinctions among genuine approval of acts of self-help, reluctant acquiescence in them and resigned recognition of a fait accompli." (11) Therefore, the discussion that follows is necessarily speculative and, indeed, somewhat tentative. (12)

    Nevertheless, states certainly do make threats, in a manner analogous to a use of force in self-defense, in response to a prior use (or threat) of force against them. (13) The question, then, is whether such threats should be considered lawful and, if so, on what basis. In tackling that question, it is important to note that this Article does not propose a reform of the current legal regime. Instead, it examines whether the existing framework already provides for the lawfulness of threats of force in the context of a defensive response and how the regulation of such actions should be explicitly assessed.

    Part II briefly sets out the nature and scope of the prohibition of the threat of force in international law and its relationship to the prohibition of the use of force. Part III outlines the key traditional criteria for self-defense. Part IV examines whether the notions of non-forcible self-defense, generally, and self-defense by way of a threat, specifically, are even conceptually possible. It concludes that there is nothing to preclude states from manifesting self-defense in this way and, moreover, that countervailing threats are a logical aspect of the existing system. Part V argues that the threat of force in self-defense is not only conceptually possible under the current law, but that it is a desirable feature of it. Finally, Part VI examines how such a manifestation of the right of self-defense may be regulated, based on the existing criteria for self-defense as commonly understood.


    The absolute prohibition against the inter-state threat of force is contained in the first limb of Article 2(4) of the UN Charter. It Unfortunately, Article 2(4) itself offers little concrete guidance as to what conduct triggers a breach of the prohibition of the threat of force. Indeed, the Charter remains silent as to how international law defines (or should define) a threat of force. This deficiency has led to academic debate as to what a threat of force actually entails and at what point a "threat" violates Article 2(4). (15) To constitute a breach of the prohibition, must a threat of force be delivered as a classic verbal ultimatum--"comply or else"? Can nonverbal actions, such as conducting military exercises, also constitute threats of force in prima facie violation of the prohibition? This second question is particularly relevant to the relationship between threats and self-defense: a state may nonverbally communicate a defensive threat, for example, by positioning troops on its borders. (16)

    This Part briefly sets out general understandings of the threat of force as regulated by international law. It first considers the legal source of the prohibition of the threat of force, through reference to the UN Charter and other quasi-statutory material. It then considers the extent to which the ICJ has examined the threat of force and highlights how the Court has conceptually "coupled" threats with the use of force. Finally, this Part sets out a typology of threats to use force that states may make in international relations.

    1. The Source of the Prohibition of the Threat of Force

      Like the prohibition of the use of force, the prohibition of the threat of force is binding on all members of the United Nations because it is explicitly provided for in Article 2(4) of the UN Charter: "All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other...

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