Unipolarity and the increasing frequency of US military intervention

Abstract Ever since the end of the Cold War, scholars have debated whether unipolar international systems promote peace or foster conflict. Yet decades later, the empirics of this question remain underexplored, as the debate has mostly been addressed from a theoretical perspective. We advance this debate by systematically comparing the frequency of US military interventions abroad during the bipolar Cold War (1945–1990) and the unipolar post-Cold War era (after 1990). To do so, we use novel data from the Military Intervention Project, a comprehensive dataset of all US foreign military interventions between 1776 and 2019, measuring the US threat, display and usage of force abroad, as well as its engagement in wars. We apply ARIMAX statistical models that account for the impact of prior US military interventions, core theoretical variables and polarity shifts on intervention patterns across time. We find that US military intervention increased significantly in frequency after 1990, suggesting a structural shift in intervention patterns following the transition from bipolarity to unipolarity. Thus, unipolarity may prod its hegemon—although not necessarily the system as a whole—into more numerous militarized disputes. These empirical findings carry important policy and theoretical implications for US grand strategy and security into the future.