Recent work in comparative politics and international relations has shown a marked shift toward leaders as the theoretical unit of analysis. In most of the new theoretical models a core assumption is that leaders act to stay in power. There exists, however, remarkably little systematic empirical knowledge about the factors that affect the tenure of leaders. To provide a baseline of empirical results we explore how a broad range of domestic and international factors affects the tenure of leaders. We focus in particular on the effect of conflict and its outcome. We find that political institutions fundamentally mediate the costs and benefits of international conflict and that war is not necessarilyex postinefficient for leaders. This suggests that the assumption that war isex postinefficient for unitary rational actors can not be simply extended to leaders. Therefore, a focus on leaders may yield important new rationalist explanations for war.