Walzer argues that across geographical jurisdictions and historical time, ideas about the proper conduct in wartime are incredibly consistent. He is referring to moral judgments made by ordinary people, not sets of laws. This sense of morality, of right and wrong, is grounded in a belief in human rights. Throughout history, this commonly held morality has influenced decisions about just and unjust wars as well as ways of fighting.

Aggression or the unprovoked attack of a sovereign state is considered a moral crime, and victim states have a right of self-defense. States also have rights of territorial integrity and political sovereignty, even if their boundaries were established through unjust means. Walzer allows for just military intervention in such states in very limited circumstances, such as egregious violations of human rights in the form of massacres and enslavement.

A common aspect of morality throughout time is that although people are killed in wars, certain acts, such as mass rape and massacres of civilians, elicit outrage. They are indefensible and morally wrong for both aggressors and defenders. Seeing a soldier’s human side in wartime makes combatants reluctant to kill; Walzer highlights the reluctance of soldiers to kill enemy soldiers when unaware and engaged in non-threatening activities, such as bathing.