The "imminent threat" requirement for the use of preemptive military force: is it time for a non-temporal standard?

• Author: Rockefeller, Mark L.

For centuries, international law recognized that nations need not suffer an attack before they can lawfully take action to defend themselves ... scholars and international jurists often conditioned the legitimacy of preemption on the existence of an imminent threat--most often a visible mobilization of armies, navies, and air forces preparing to attack. (1) Under customary international law, a state may use preemptive military force only if faced with an imminent threat. (2) The concept of imminence is traditionally understood in a temporal sense--that is, imminent is nearly synonymous with immediate. Thus, a preemptive strike may generally only take place immediately prior to the attack it is intended to thwart. Put another way, the nearness of the impending attack determines the appropriateness of a preemptive strike.

We now live in an age of terrorism and "uniquely destructive weaponry," (3) such as Weapons of Mass Destruction (WMDs). (4) The capabilities of the Al-Qaeda (5) network and the willingness of terrorist organizations to cause calamitous harm are as clear as the images seared into the minds of television viewers around the globe on September 11, 2001.

The issue therefore arises: Do modern technologies make waiting for a visible "mobilization of armies" unrealistic? Do terrorist tactics necessitate a broader interpretation of imminence by the international community? Could a nontemporal standard adequately assure the necessity of the use of preemptive force and that other, non-forceful options have been exhausted?

This article explores whether the traditional temporal interpretation of imminence should be changed. The article argues for an improved standard--one that retains the requirement for necessity, while eliminating the outmoded requirement for immediacy. It argues that modern weaponry and terrorist tactics countermand the current time-based standard. Part I gives background information, a history of the current understanding of imminence in international law, the evolution in weaponry, and an overview of current state behavior relative to the existing standard. Part II analyzes why a temporal interpretation of imminence may be outdated, reviews current scholarship in the field, and notes other areas of law in which the concept of imminence is understood nontemporally. Part III suggests an alternative approach, describes the components of such an approach, and discusses its relative strengths and weaknesses. Finally, Part IV summarizes and gives recommendations for the implementation of this new standard.

1. BACKGROUND

   While Articles 2(3) and 2(4) of U.N. Charter broadly prohibit the use of unilateral military force, Article 51 provides an exception for instances of self-defense. (6) Considered an "inherent right" (7) for states, self-defense is the only justifiable rationale for the use of armed force without U.N. Security Council approval. (8) Self-defense is an established doctrine. However, the legality of the use of force in self-defense to thwart an attack before the attacker fires the first shot (i.e. preemptive military force) is hotly debated. Scholars disagree on whether preemptive force is permissible at all under a strict interpretation of Article 51 and struggle to reconcile prohibitions on the use of force with actual state practice.

   Customary international law requires that force, when used, "comply with three basic criteria--necessity, proportionality, and imminency." (9) In this paper, I will not discuss proportionality. I shall assume that a state adheres to this doctrine in any use of force it applies--be it preemptive or otherwise. Similarly, necessity will only be discussed within the broader concept of imminence. This article focuses, rather, on the legality of a specifically preemptive action, the concept of imminence, and its inadequacy to meet contemporary threats.

   To conceptualize this issue, it is useful to think of a timeline, with the occurrence of the armed attack at the center and lines extending into the past and the future. Given this framework, the current standard of imminence requires that an anticipatory attack be close to the center of the timeline; that is, near to the time at which the actual armed attack would occur absent intervention. (10) Please keep this conceptualization in mind as we explore the history of the current standard.

   1. History, Evolution and Ambiguity of the Imminent Threat Requirement

      The classic definition of imminence governing the use of preemptive force is found in the famous Caroline incident. On December 29, 1837, approximately eighty British soldiers crossed the U.S. border into New York from Canada and seized a small steamer known as the Caroline. (11) Canada was a British colony, and British forces believed that rebels attempting to overthrow the Crown were using the vessel to support raids into Canada. Acting in "self-defense," the British crossed into U.S. territory, stormed the ship, set it on fire, and sent it over Niagara Falls. (12) Protesting the incident, U.S. Secretary of State Daniel Webster argued that in order to legitimately claim self-defense, the British must have had "necessity of self-defense, instant, overwhelming, leaving no choice of means, and no moment of deliberation." (13) To those who believe preemptive self-defense is legally justifiable, this classic temporal definition still applies today. (14)

      It is important to note, however, that the legality of preemptive force as a legal concept is not codified in the U.N. Charter, even though the principle has been recognized by international legal bodies as customary international law. For example, the Caroline standard was relied on by the International Military Tribunal at Nuremberg, by the International Court of Justice in its Nicaragua decision, and by the International Court of Justice in its advisory opinion on the Use of Nuclear Weapons. (15) Thus, there exists general agreement that preemptive military force is acceptable under customary international law if the threat is imminent. (16)

      But this classic standard has not remained static. For example, during the Cold War, a polarized world and the threat of nuclear holocaust led to the suggestion that the traditional concept of immediacy adjust to a more liberal understanding of imminence--one that aligned with mid-twentieth century state practice. (17) In the opinion of some, it was President John F. Kennedy and the Cuban Missile Crisis in 1962 that manifested a shift in the U.S. policy of preemption. (18) The Kennedy Administration's use of a "quarantine" against Cuba was technically a blockade--arguably, a preemptive act of aggression. (19) Yet, in hindsight, the blockade was generally viewed positively by the international community as a "cautious, limited, and carefully calibrated" response. (20) Thus, as early as the 1960s, an evolution in the Caroline standard was evident.

      The ambiguity of the imminent standard, as reflected in the inconsistent international reactions to acts of preemption, supports a call for further evolution. For example, in 1967, Israel, surrounded by opposition forces, initiated a preemptive first-strike against Egypt. (21) The United Nations did not condemn Israel's preemptive action (it only asked Israel to return the conquered territories), because Israel's use of force was deemed to be sufficiently necessary--that is, the Egyptian threat was considered to be imminent. (22) Yet in 1981, Israel performed preemptive air strikes once again, this time against an Iraqi nuclear plant. (23) Here, Israel's claims of "self-defense" fell on deaf ears. The U.N. Security Council unanimously condemned the attack, because it doubted the imminence of the threat posed by the incomplete reactor. (24) Israel's 1981 attack was viewed as being without legal basis, and the distinction between the 1967 and 1981 attacks was ostensibly reasonable. In contrast, however, consider Operation Desert Fox, a 1998 four-day British and American bombing campaign against chemical and biological weapons facilities in Iraq. (25) The potential use of, or target for, Iraq's weapons was unknown. Only speculation linked the threat to British or American interests--a chemical or biological attack was not imminent, in the traditional sense. Yet, Operation Desert Fox was not condemned by the U.N. Security Council; tacit approval was given for the preemptive use of force in order to counter a threat which was not yet demonstrated to be imminent. (26) Thus, conflicting international reactions to state practice, in seemingly analogous situations, represent ambiguity in the traditional standard used to determine what constitutes an imminent threat.

   2. Evolution in Weaponry

      On a parallel timeline, the weapons of war have evolved. In modern warfare, a single attack can be instantaneous and devastating. As U.N. Secretary General Kofi Annan stated regarding September 11th, 2001, "it is hard to imagine how the tragedy could have been worse. Yet, the truth is that a single attack involving a nuclear or biological weapon could have killed millions." (27) It has become increasingly clear that terrorists, fueled by the desire for mass casualties and increased media attention, are more and more willing to use devastating technologies. (28)

      Proliferation of nuclear materials adds to this concern. The post-Cold War disintegration of the Soviet Union, with the accompanying economic and political tribulations, created a market for WMDs and associated materials. (29) This era similarly gave rise to an increase in rogue states and transnational terrorist groups. (30) Indeed, the potential of such groups to acquire WMDs is greater now than at any other time in history. (31) The risk is profound.

      Consider the capabilities of modern weapons. For example, beginning in March of 1988, the Iraqi military, using a combination of artillery and air forces, dumped chemical agents on Kurdish cities in northern Iraq. (32) Experts...