On the heterogeneity of terror

•The first paper to propose to look at terrorism not as a uniform phenomenon.•Classifies terror according to ideology (left, right, separatist, Islamist, etc.).•Argues why terror patterns are different across ideologies.•Shows strong differences in the determinants of terror across terror types.•Shows major shifts over time.

Most of the existing literature on the determinants of terrorism treats terror as a uniform phenomenon and does not distinguish between different types of terror. We argue that terror of different ideological types should have different determinants as the terror groups cater to different grievances, engage in compromise to different degrees and have different organizational constraints. We explicitly address the heterogeneity of terror by classifying groups according to their ideologies and, using the Global Terrorism Database, show that the determinants of terror differ strongly between terror types.