The personal costs of war — military dead and injured—are the most salient measure of war costs and the primary instrument through which war affects domestic politics. We posit a framework for understanding war initiation, war policy, and war termination in democratic polities, and for understanding the role that citizens and their deaths through conflict play in those policy choices. We believe that war support derives from individuals’ calculations of a war’s value and cost. High-value conflicts are more likely to be supported than low-value conflicts. Conversely, low-cost conflicts are more likely to occur andtohave durable support, while high-cost conflicts are likely to see rapid erosion of support when they are fought. We develop a comprehensive theoretical approach and examine these arguments with a variety of empirical methods in multiple wars, conducting analyses of tens of thousands of citizens across a wide variety of historical and hypothetical conditions. We also analyze the ways that military casualty information travels from distant battlefields to the homefront and address policy implications.