NATO enlargement and US foreign policy: the origins, durability, and impact of an idea

Since the Cold War, NATO enlargement has moved from a contentious issue in US foreign policy debates to an accepted plank in US strategy. What explains this development—why has support for enlargement become a focal point in US foreign policy? After first reviewing US policy toward NATO enlargement, this article evaluates a range of hypotheses from international relations theory and policy deliberations that might explain the trend. It finds that no one factor explains the United States’ enlargement consensus. Instead, pervasive US support for enlargement reflects the confluence of several international and domestic trends that, collectively, transformed NATO expansion into a lodestone of US foreign relations. Regardless, the development carries a range of consequences for US national security; although enlargement afforded the United States significant oversight of European security and political developments, it came at the cost of increased tensions and diminished flexibility with Russia, allied cheap-riding, and US overextension.