Cody Marden, Vol. 37 Associate Editor
In November 1983 the North Atlantic Treaty Organization (NATO) conducted a ten day military exercise known as Able Archer 83. This exercise was arguably the closest the world has ever come to WWIII. The realistic nature of the exercises, combined with the deteriorating relations with the U.S., led many in the USSR to suspect that Able Archer could be a ruse that was actually obscuring preparations for a U.S. first strike. In response to the exercises the USSR placed their nuclear arsenal on standby and placed air units in East Germany and Poland on alert. Luckily, the situation defused itself with the end of the NATO exercise.
What if the Soviet Union had preemptively attacked the U.S.: would the attack have been legal under international law? The answer is not entirely straightforward. The actions of states that act in anticipatory self-defense are measured by somewhat subjective principles. However, there are instances where military exercises could constitute sufficient provocation to conduct an anticipatory attack under international law.
The international framework for anticipatory self-defense arises from two sources: Article 51 of the U.N. Charter and the Caroline Test of customary international law. Beginning with Article 51, the Charter states in part that “[n]othing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations.” Although the Charter limits self-defense to instances involving armed attacks, the wording of the Charter has been read not to influence the right of self-defense under customary international law. This being the case, nothing in the Charter excludes the right to take to anticipatory action.
The Caroline Test, a principle of customary international law, was developed following a preemptive attack by British forces on a U.S. steamer, named the Caroline, which was supporting insurgents in British Canada. Following the incident U.S. Secretary of State Daniel Webster responded, in part, by establishing a narrow test to determine where anticipatory self-defense is justified under customary international law. Webster described that anticipatory self-defense is justified when the threat is “instant, overwhelming, and leaving no choice of means, and no moment for deliberation.” Modern scholars have chosen to read the Caroline Test as having two distinct prongs: (1) the use of force must be necessary, because a threat is imminent and all peaceful alternatives have been exhausted; (2) and the use of force must be proportionate to the threat.
The problem with applying the Caroline Test is that there is ambiguity in determining whether prerequisites for action exist. In most cases involving the use of force the international community has allocated the evaluation of when use of force is appropriate to the Security Council. However, the Caroline Test relies on the nation conducting the attack to make the determination of when an attack is warranted. This is obviously problematic because the nation conducting the attack will likely feel the potential provocation more acutely than an impartial actor.
In no place is this more true than in determining whether an attack is “necessary.” Necessity is a reaction to a “clear and present danger of an imminent attack, and not mere general preparations by the enemy.” A textbook example is the 1967 Arab-Israeli War, where Israeli conducted an anticipatory attack in the response to both the rhetoric of Egyptian politicians and the buildup of Egyptian forces along its border. It is now theorized that Egypt never intended to attack Israel – that the build was just a show of force. Unfortunately Israel perceived the threat to its sovereignty to be credible enough to warrant use of force.
In this sense the textbook example is very similar to conditions that could produce a legal response to a military exercise. If the state under threat reasonably misconstrues the threat presented as being credible, this could lead the state to determine that the use of force would be necessary under the Caroline Test. It would not be hard to imagine, for instance, that a military exercise by North Korea in the DMZ combined with incendiary remarks could put South Korea in a position where it would feel they are under imminent threat and need to conduct an anticipatory action.
A further hitch in this analysis is that the calculus will be affected by different categories of threats. For example, in 1967 Israel could afford to wait until almost the last possible moment to launch its preemptive strike. But take the Able Archer example, where nuclear weapons were in play: nuclear attacks, unlike potential conventional attacks, are much harder to stop once launched. Under the best case scenario, a nation would have minutes to intercept a plane or missile carrying a nuclear warhead. The potential harm of a nuclear weapon is so great that a state might determine that it simply cannot wait to act. In a military exercise involving nuclear weapons, it would be much more likely for a state to believe it is faced with an actionable threat.
In conclusion, the ambiguity inherent in the application of anticipatory self-defense under customary international leaves potential for states to respond to military exercises that they reasonably misconstrue as presenting a credible threat. Because the state evaluating the threat is the state under threat, this state will often overestimate the level of danger leading to potentially tragic consequences.
 Benjamin B. Fischer, A Cold War Conudrum: The 1983 Soviet War Scare, http://1.usa.gov/1SUDAKM (2007).
 U.N. Charter, art. 51.
 Letter of Mr. Webster, Secretary of State, United States of America, to Mr. Fox, British Ambassador to the United States of America (April 24, 1841), in 29 BRITISH AND FOREIGN STATE PAPERS, 1840-41 at 1137-38 (1857).
 Some scholars have implied additional conditions. See Leo Van den hole, Anticipatory Self-Defence Under International Law, 19 Am. U. Int’l L. Rev 69, 97 (2003) (“[I]t seems reasonable to add two more conditions: first, an action of anticipatory self-defence will only be justified if the U.N. Security Council has not yet been able to take affirmative action, and second, the state against which the right of anticipatory self-defence is being
exercised has to be in breach of international law.”).
 See generally U.N. Charter Chapter VI; U.N. Charter Chapter VII.
 Van den hole, supra note 6 (“The decision to use force in anticipatory self-defense is generally conditioned reflex to stress.”).
 See id. at 100. (“After the Soviet Union falsely reported to the United Arab Republic (“UAR”) that Israel was planning a major attack on the UAR, President Gamal Abdel Nasser took several very provocative actions: the UAR moved a force large enough to conduct offensive operations into the Sinai; Nasser publicly made statements that he intended to eliminate Israel; the UAR dismissed the U.N. emergency force from the Sinai; and the UAR closed the Straits of Tiran to Israel.”)
 See Avi Shlaim and William Roger Louis, The 1967 Arab-Israeli War: Origins and Consequences 68-69 (2012).