International arms sales play an important role in the defense of states and as a result a sizeable literature has developed that deals with this topic. The importance of arms sales to states has carried over into political science as a result, where weapons play an important role in a variety of theories particularly those that fall into the various realist camps. Most of this literature focuses upon states that produce and sell arms with a significantly smaller literature dealing with states that purchase, rather than produce, them. This unfortunate gap in the literature prevents a complete understanding of international arms sales as the decision making process of arms purchasing states is currently almost completely discounted. This dissertation develops a theory of the strategic logic of arms purchasing. The theory laid out here suggests that states that must purchase arms weigh costs and benefits before selecting certain arms suppliers over others in the greater international arms market. This decision is largely based upon the perceived need for weapons based on the likelihood of conflict in the near future versus the dependence associated with purchasing the arms. The dependence associated with arms purchases can be reduced by purchasing arms from multiple arms producers at the cost of logistical efficiency. The theory laid out here is then tested via a pair of comparative historical case studies. These case studies analyze a state’s history in terms of geopolitical alignment with its major arms suppliers and its perceived probability of conflict. Predictions are made based on the theory and these predictions are then tested by developing networks, graphs, and charts based on the Stockholm International Peace Research Institute’s Arms Transfers Database and the U.S. Department of State’s Bureau of Arms Control, Verification and Compliance’s World Military Expenditures and Arms Transfers series of reports. The first comparative historical analysis covers Iran and Iraq during roughly the time period before and during the Iran-Iraq War while the second comparative case study analyzes Finland, Czechoslovakia and the Czech Republic during the lead up and aftermath of the collapse of the Soviet Union. The theory performs well in predicting the actions of the states in the case studies suggesting that arms purchasing states balance need for weapons against the dependence associated with the arms purchases.