Abstract: Motivated by strategic competition between the United States and China in East and Southeast Asia, this project examines how smaller countries choose between an established power and a rising challenger. I develop a dynamic model in which two major powers compete for the political alignment of a smaller country. While the established power can immediately enforce its preferred policies, the challenger must gradually build political influence through repeated cooperation. In the absence of self-enforcing agreements, preliminary results suggest that smaller countries may strategically switch alliances over time. I next examine how self-enforcing agreements shape alliance formation and whether smaller countries can sustain long-term partnerships that improve their bargaining position by moderating the policy demands of competing great powers.