In 2018, more than half of all people killed in the 34 countries suffering from civil war died in Afghanistan or Syria. Why do some civil wars become more severe than others? Surprisingly, our knowledge on this pertinent question is limited. First, while previous research has identified some factors that drive the death toll upwards, our understanding of the factors that restrain escalation and depress the body count remains narrow. We emphasize both causes of escalation and restraint and explore how actor characteristics, institutions, and norms restrain actors’ use of violence. Second, earlier scholarship tends to compare the most severe civil wars to all others. In contrast, we break new ground by identifying civil wars that saw low severity despite a high risk of escalation. Comparing these cases to more severe civil wars will yield new insights on the sources of restraint in civil war. This project seeks to both build and test theory. To develop a theory of how factors interact to influence civil war severity, we will compare Sudan (Darfur) and Côte d’Ivoire, and conduct a Qualitative Comparative Analysis (QCA) of an intermediate number of cases. To test the theory, we will employ process tracing on cases selected from the QCA to examine temporal and spatial variation, and conduct a global statistical analysis of civil war severity. Deepening knowledge on restraint in civil war is crucial for building resilient societies and contain existing civil wars.