This dissertation examines why some states develop conscript militaries while others rely solely on volunteers. I argue that two variables determine what recruitment decisions states make when initially designing their military. First, either domestic or foreign policymakers can dominate the decision-making process. These actors often have different perceptions about the military’s most important goals and how to achieve them. When foreign powers view new states as sufficiently important enough to their interests, recruitment policies reflect their preferences, rather than those of domestic policymakers. Second, the threat perception of the actor making recruitment policies affects how they approach military design. Major external threats to the new state’s territory constrain recruitment options in the interest of immediate defense, leading to conscription, while lower threat environments permit more freedom to adopt different practices. I test this argument using an original dataset of 224 cases of state creation and major regime change from 1918–2011, including original variables that measure different types of foreign military influence. I also use qualitative evidence—including archival documents and interviews—to conduct a series of case studies focusing on the Middle East and Europe that are designed to control for alternative hypotheses and establish the causal processes. The results support my initial hypothesis, demonstrating that military design is often affected by hierarchy in international relations. This research suggests important lessons for policymakers interested in effecting military reform by highlighting a role for foreign security assistance in processes of military design.