Political institutions, resources, and war: Theory and evidence from ancient Rome

How does a governing coalition's size affect the extent and type of violence in society? The model developed here predicts that larger coalitions are less likely to fight for private goods (e.g., plunder) than for public goods (e.g., defense), yet this substitution need not reduce the overall scale of fighting. That prediction is tested by investigating how Rome's transition from Republic to Empire affected military patterns. The raw data and three empirical tests suggest that the Republic engaged in more battles overall and that Republican battles had more of a public goods component. This study furthers our empirical knowledge about the ancient world while bringing data to bear on contemporary debates about the causes of peace and war.