This article considers the ideational fabric of American empire. Section one discusses why liberal democratic empires are not particularly peaceful. Section two highlights the analytical value of a focus on U.S. strategic culture in explaining U.S. military practice. Section three looks more broadly at the role of identity in giving meaning to the U.S. imperial project and in giving reasons for the use of force in support of it. Throughout, comparisons are made with the British Empire and consideration is given to the meta-theoretical options and methodological challenges for the social science of strategic culture.