1 This policy was set forth in 2002 in “The National Security Strategy of the United States of America” (September 2002); available at http://www.whitehouse.gov/nsc/nss.pdf. The Bush administration has referred to the policy as one of preemptive use of force, but, as many commentators have pointed out, it is instead preventive, since a use of force is preemptive only when the aggression to which it is a response is imminent. The preemptive/preventive distinction is discussed further below.
2 Allen, Buchanan and Keohane, Robert O., “The Preventive Use of Force: A Cosmopolitan Institutional Proposal,” Ethics & International Affairs 18, no. 1 (2004), pp. 1 – 22 . All in-text citation references are to this article.
3 Another kind of intervention is humanitarian intervention, where the purpose is not to avoid an attack on the intervener, but rather to avoid massive human rights violations against the citizens of the target of the intervention. I argue later that it is a mistake to treat these two forms of intervention as morally akin.
4 Humanitarian intervention would be an exception to this.
6 On this point, see Luban, David, “Preventive War,” Philosophy & Public Affairs 32, no. 3 (2004), p. 227.
7 Again, excepting cases of humanitarian intervention.
8 These two conditions are related. If the expected aggression has yet to be initiated, defensive force is generally not a last resort.
9 This also explains why someone engaging in self-defense is not permitted to harm an innocent third party. Though the third party is, like the attacker, not culpable for the attack, neither is she causally responsible for the harm inflicted by the attack. The claim that a defender is justified in defending against a nonculpable attacker is disputed, however. Jeff McMahan has argued that justified self-defense requires the moral responsibility of the attacker for the attack. See, e.g., his “Preventive War,” in Rodin, David and Sorabji, Richard, eds., The Ethics of War: Shared Problems in Different Traditions (Aldershot,, U.K. : Ashgate, forthcoming 2005).
10 The body the authors have in mind for the ex ante review of the intervention might, of course, over time evolve into a genuine judicial institution, but, given the length of time this would take, its prospect provides no legal cover for states now desiring to intervene.
11 McMahan, in “Preventive War,” makes this point, though on different grounds.
12 The authors might seek to justify preventive intervention in WMD cases by introducing into their account a feature like Michael Walzer's supreme emergency that permits an overriding of just war rules in cases where extreme harm is threatened. But Walzer's notion of supreme emergency applies at the jus in bello level, not at the jus ad bellum level where the authors need it, and the level of threatened harm constituting a supreme emergency for Walzer is much higher than the level of threatened harm in WMD cases. In addition, the adequacy of a moral theory of war that includes the notion of supreme emergency is a matter of controversy. For Walzer's discussion of supreme emergency, see Just and Unjust Wars (New York,: Basic Books, 1977), chs. 16 and 17.
14 See Luban, “Preventive War,” p. 214.
* I wrote this essay in 2003–04 while I was a Fellow at the Center for the Study of Professional Military Ethics at the United States Naval Academy. I would like to thank the Center for its support, as well as George Lucas and two anonymous reviewers for their valuable comments.