Recent research concludes fighting or losing an interstate war is not costlier for democratic leaders than dictators, which implies most of our institutional explanations for differences in conflict behavior across regime type rest on empirically tenuous assumptions. I argue military mobilization, a fundamental but often overlooked aspect of war, should be costlier for democrats than dictators. Waging interstate war is associated with higher military spending and, often, lower social spending. Variation across regime type in the representation of the general public, civilian elite, and military in leaders’ winning coalitions should make democrats more likely than dictators to lose power given wartime patterns of government spending. This argument finds support during the period from 1950 to 2001. My findings provide microfoundations for a number of existing empirical results and suggest that differences in the conflict behavior of democracies and dictatorships should be largest when waging war requires a significant mobilization effort.