This chapter and the next are devoted to jus ad bellum, the justice of war. Jus ad bellum is the morality of going to war, the morality of the decisions taken by leaders that initiate war. As the last chapter revealed, the conception of jus ad bellum in the just war tradition has changed over time. In this chapter we consider jus ad bellum in general, and under the national defense paradigm, in particular. This paradigm is the conception of jus ad bellum brought into being at the end of World War II by the post-war settlement, codified in the charter of the UN. The national defense paradigm differs most significantly from the earlier just war paradigm in its rejection of war as punitive. Under the just war paradigm, a just cause for war was “a wrong received,” making a just war a form of punishment for this wrong. Beginning in the eighteenth century, under the regular war paradigm, a sovereign ruler had the moral and legal discretion or right to go to war, so that, in effect, any cause was a just cause. A state could go to war “for a good reason, a bad reason or no reason at all.” When jus ad bellum staged a comeback in the twentieth century under the national defense paradigm, a just cause for war was limited largely to self-defense, without the punitive element. The national defense paradigm shares with the just war paradigm the moral asymmetry that justice cannot be on both sides in an armed conflict.

The main moral argument for the national defense paradigm is indicated by the opening quotation from the philosopher Montesquieu (1689–1755), who sets out the principal analogy, the domestic analogy, in terms of which the paradigm is both understood and morally justified. The domestic analogy is an analogy between states and individuals, and the analogical argument based on it is that because states are like individuals and individuals have a moral right to use force to protect themselves against attack, states do as well. The analogy is called domestic because it compares the international arena which states inhabit to the domestic arena inhabited by individuals within a state. Political philosopher Michael Walzer relies prominently on the analogy in his account of jus ad bellum. The analogy involves, he notes, a comparison “of personal liberty and political independence.” As an attack by an individual interferes with the victim’s personal liberty, aggression by a state interferes with the victim state’s political independence. In both cases, attacks are prohibited and, if they occur, force in self-defense is morally justified.