Initiating war is a crime called aggression, and when attacked, people are justified in forcefully resisting in defense of their lives and rights. The most important moral judgments about war are grounded in the rights of individuals even though the justification for defense is based on the collective rights of territorial integrity and political sovereignty. Walzer believes boundaries must be respected even if they originated from unjust conflict.

This legalist paradigm, dubbed the theory of aggression, “first takes shape under the aegis of the domestic analogy” (61), in which the international order is compared to the civil one. Aggression, therefore, conjures images of murder and armed robbery. Walzer summarizes the theory in six propositions: First, an international society of independent states exists, and it is assumed that other states do not intervene in the internal affairs of such states. Second, this international society has a law that establishes the rights of territorial integrity and political sovereignty. Third, any use of force or imminent threat of force by one state against another is a criminal act. Fourth, such aggression justifies two types of violent response, one by the victim and the other by the victim and other states.