This dissertation is composed of three independent essays devoted to the study of the duration of military alliances. In Chapter 2, I investigate how the power distribution and the geographical distance between allies interact and affect alliance duration. I find that geographically remote and unequal alliances are more likely to endure than geographically close and unequal alliances. In Chapter 3, I examine how the economic dependence of weaker states on their major power allies and their capability change interact and affect alliance duration in asymmetric alliances. I find that alliances with minor powers whose capabilities increase and whose economic dependence is low tend to terminate earlier than those with minor powers whose economic dependence is high. In Chapter 4, I undertake a case study of the U.S.-South Korean alliance. I find that the U.S.-Korean military alliance is deeply embedded in the socioeconomic structure of Korean society generated by export-led growth and its economic dependence on the U.S, consequently making the U.S.-ROK alliance more resilient.