What explains the emergence of leftist rebel groups? I provide one explanation for their origins in colonized and recently decolonized countries during the Cold War. In this context, I argue that imperial assimilatory education programs terminating in the metropole facilitated the rise of a would-be rebel leadership cadre committed to leftist ideas and connected to leftist activists, and this cadre ultimately made the formation of a leftist rebel group more likely. Relying on archival and primary materials, I focus on variation in educational experiences of rebel leaders in Eritrea’s Independence War to qualitatively evaluate different explanations for the formation of groups with different ideologies. I probe generalizability quantitatively with a global sample of civil wars, as well as qualitatively with an overview of cases colonized by Portugal using archival data from three countries.