This dissertation explores civil-military relations in democratizing contexts, specifically how the historical relationship between the military and the broader public shapes responses to political crises such as riots and revolutions. I develop a novel theory, rooted in civil-military relations literature from political science and sociology, for how an army’s historical interactions with the population and with foreign sponsors create doctrine by shaping organizational culture and practices toward the population. Doctrine, in turn, influences the military’s response to a popular uprising. The foundations of military doctrine are historical and include the military’s institutional origins, role in national independence, and relationship to the ruling party. Subsequently, doctrinal innovation occurs as a result of interacting with the domestic population and foreign military sponsors. The dissertation features qualitative case studies of Tunisia, Egypt, and Syria during the Arab Spring and a quantitative data analysis of major uprisings worldwide since 1950. Both qualitative and quantitative evidence demonstrate that the nature of military doctrine explains soldiers’ behavior during popular uprisings better than alternative arguments based on capacity, patronage, and ethnicity.