The number of multinational military exercises—that is, military training events between two or more states—has grown dramatically since the end of the Cold War. Moreover, many of these training events involve non-allies and serve functions other than deterrence or preparation for war. Why do major powers conduct military exercises with non-allies and why have these training events increased since the end of the Cold War? Training has remained a vital military activity since the advent of war but the purpose of holding exercises has evolved over time. States traditionally use military exercises to deter or prepare for war, yet since the end of the Cold War major powers have increasingly employed training events as a ‘non-war’ means to shape their strategic environments by influencing partners and rivals. I argue that major powers conduct multinational exercises with non-allies in order to reduce strategic uncertainty; moreover, exercises have grown since the end of the Cold War due to an increase in uncertainty wrought by the rise of violent non-state actors, as well as the habitual nature of military cooperation. This dissertation offers a novel understanding of military behavior in the post-Cold War environment in which interstate war is rare but the persistent threat and consequences of terrorism, ethnic war, transnational crime, and natural disasters seems unending. I test my argument with both quantitative and qualitative methods using a new dataset, in-depth interviews, large-N regressions, and illustrative case studies. This dissertation seeks to provide an update to the traditional works in military doctrine by highlighting the important role of shaping operations in the post-Cold War era and how these types of military activities affect international security.