When are states justified in using military force in anticipation of an “armed attack” that has yet to occur? Must they wait, as stipulated by international law, for an armed attack either to occur or to be so “imminent” and so “overwhelming” in its necessity as to leave “no choice of means” and “no moment for deliberation”? Are there any circumstances under which it is justified to launch a preventive strike to forestall the development of a more serious future threat? Must states wait for legal authorization from the United Nations Security Council, or are they justified in taking unilateral action in certain situations?

Michael Doyle addresses these critical questions in Striking First, which includes an introduction by Stephen Macedo and thought-provoking dialogues with Harold Koh, Richard Tuck, and Jeffrey McMahon. Doyle notes the new security threats resulting from the proliferation of nuclear weapons and the emergence of nondeterrable nonstate actors. He argues that preventive responses to these threats are subject to too few constraints by the Bush Doctrine and too many constraints by international law. In a new theory of anticipatory self-defense, he accepts existing international legal standards justifying preemptive responses to imminent threats and develops a jurisprudence for preventive responses to more distant threats.

Doyle proposes four standards for the evaluation of military or other coercive responses to nonimminent threats: lethality, likelihood, legitimacy, and legality. Lethality refers to the extent and irreversibility of the anticipated harm. Likelihood refers to the probability that the adversary will implement the threat. Legitimacy includes traditional just war criteria of proportionality, necessity, and deliberation (including many diverse voices in the decision). Legality refers to the behavior of both the adversary and the preventer. Any state contemplating preventive action must attempt to secure multilateral authorization through the Security Council, though Doyle argues that unilateral prevention is sometimes warranted.

This is an extraordinarily useful framework for evaluating preventive action in a complex world involving difficult choices. Doyle's movement beyond a strictly legalistic approach to allow unilateral actions after a good-faith effort at multilateral deliberation is particularly welcome, given the often politicized nature of the Security Council. It helps to narrow the gap between a normative/legal theory of when states can act preventively and a positive/explanatory theory of when states actually do act preventively.

I should note in this regard that a preventive war strategy does not necessarily require “striking first.” Preventers want war now rather than war later, but for domestic political or diplomatic reasons, they sometimes prefer to provoke their adversaries into striking first. This adds a slight complication to assessments of legitimacy and legality, but Doyle's criteria are flexible enough to handle such cases.

The author applies his framework to United Nations sanctions against South African apartheid, the American “quarantine” in the Cuban Missile Crisis, the 1981 Israeli attack on Iraq's nuclear reactor, and other cases. Most of his judgments come across as quite balanced and reasonable. For example, he classifies Israel's 1981 preventive strike in the middle range of justifiability across each of his four indicators, in contrast to the condemnation of the action (without a U.S. veto) by the UN Security Council. His reasoning is sound, though I would have ranked the lethality of the threat in the highest category, given his estimate of 100,000 Israeli deaths from a single Iraqi bomb against Tel Aviv. In addition, a more thorough treatment of the Israeli case, and indeed any case of preventive attack to block a state from crossing the nuclear threshold, would need to give more attention to the feasibility of relying on deterrence as an alternative strategy.

The relevance of alternative strategies is subsumed under Doyle's theoretical discussion of the necessity component of the legitimacy criterion and of the legal requirement to seek redress through multilateral channels, but I would give it more prominence. I think the author would agree that any evaluation of the justifiability of an Israeli preventive strike against Iran, for example, would have to consider the feasibility of relying on deterrence instead, though he neglects this point in his brief discussion.

With regard to the Cuban Missile Crisis, Doyle argues that the U.S. quarantine was justifiable (though a blockade and, hence, an illegal act of war), but that any U.S. air strike would not have been justifiable because of the risk of escalation to nuclear war. This raises difficult issues. His argument implies that the threat of an air strike would have been unjustifiable. Perhaps, but this is somewhat paradoxical in light of the common argument that the threat of escalation, based in part on quite visible preparations for an invasion that would have included airstrikes, was the primary reason that Nikita Khrushchev agreed to remove the missiles, ensuring a peaceful outcome to the crisis. What if Khrushchev had refused to withdraw the missiles? The possible justifiability of an air strike and invasion would need to be explicitly compared to that of alternative strategies. Would it have been reasonable to leave the missiles in place and rely on deterrence of their use, given that the vulnerability of the missiles in Cuba would significantly increase crisis instability and the probability of preemption? True, Kennedy was considering going to the UN and offering to trade U.S. missiles in Turkey for Soviet missiles in Cuba as a last resort, but one can easily imagine another scenario in which leaders face an implacably hostile adversary without an easy solution. What if all options are bad? We need additional criteria for choice based on the relative justifiability of alternative strategies.

Striking First, which reflects both the knowledge of a distinguished scholar and the experience and judgment of a practitioner (Doyle was UN assistant secretary-general under Kofi Annan), is an indispensable book for those interested in the question of the justifiability of preventive action against future threats. Given the omnipresence of those threats, that should include all of us. Doyle's careful reasoning and balanced judgments also make this enormously thought-provoking book perfect for the classroom.