The "democratic peace"-the proposition that liberal democracies seldom if ever go to war against one another-has forced scholars to reconsider the roles of liberal norms and democratic institutions in international security. Most scholars either believe democratic peace is genuine, or, following the realist school of international security, argue that it is spurious and that liberal democracies are no different from other states. I argue that both camps are wrong: there is no objectively delineable zone of democratic peace, but liberalism does affect the occurrence of war. A democratic zone of peace is not identifiable a priori because of the confounding role of perceptions. States that scholars label liberal-democratic do not always perceive one another as liberal-democratic, and therefore may not be hindered from war by liberalism. Yet, when liberal elites do perceive a foreign state to be liberal by their own standards, they usually oppose war with that state for ideological reasons-e.g., a wish to support fellow liberals or to uphold human rights; and when they perceive a foreign state to be illiberal, they often favor war with that state. Domestic liberal institutions, especially free discussion and elections, translate these positions into foreign policy during crises. I show how this synergism of liberal ideology and institutions worked in preventing Great Britain from intervening in the U.S. Civil War.