Why are some wars deadlier than others? Arguments from bargaining models of war and empirical analyses of war duration suggest two mechanisms to explain how many fatalities states will be willing to suffer in a war: (1) states will fight to the extent necessary to resolve the underlying causes of war, or (2) states will fight until a purely military resolution to a conflict is reached. Empirical analysis provides limited evidence in support of these explanations. However, model predictions show that these theoretically-informed models match real-world observations fairly well. In-sample predictions capture observed war dead in up to 70% cases, and out-of-sample retrospective forecasts for two wars provide reasonable estimates.