Analyses of US/Soviet arms control have usually focused on domestic variables to explain US/Soviet arms control behavior. Partly because the number of negotiating parties is only two, there is a propensity to focus on the bilateral relationship of the United States and the Soviet Union and their respective domestic political situations. Only superficial attention has usually been given to international systems variables that may well influence the domestic political situation and arms control policy. This thesis broadens the explanatory scope of US/Soviet arms control by showing how the political environment of a trilateral relationship (a subsystem that includes the West European members of NATO as a single actor as well as the United States and the Soviet Union) is a primary motivator of US/Soviet arms control behavior.