One of the most important themes in international relations is the relationship between domestic politics and interstate conflict. In this article, we use experiments to study how the human rights practices of foreign adversaries affect domestic public support for war. Our experiments, embedded in surveys in the United States and the United Kingdom, reveal several important findings. First, citizens are much less willing to attack a country that respects human rights than a country that violates them, even when the dispute concerns military security rather than humanitarian intervention. Second, human rights affect support for war primarily by changing perceptions about threat and morality. Citizens are more likely to view human rights violators as threatening, and have fewer moral qualms about fighting such countries. Our findings shed new light on the politics of war in democracies, and may provide behavioral foundations for peace among human-rights-respecting states.