During Donald Trump’s presidency and after, US foreign policy is likely to be wracked by crises. From the instability and violence in Ukraine, to the unrelenting turmoil in the Middle East, to the provocations of an increasingly dangerous North Korea, to the dangers posed by a rising China in the South China Sea and elsewhere, American policymakers are currently facing crises more numerous and geopolitically significant than at any time in a generation. Crises, however, are merely symptoms of deeper changes in the structure of global affairs. And so for the United States to meet these challenges effectively, American officials will first need to come to grips with the fact that global politics are now changing in profound ways. The fundamental fact of international politics today is that the post-Cold War era has ended, and the United States now confronts a more disordered, difficult, and contested global arena.