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.
The post-Cold War era emerged in the 1990s, after the collapse of the Soviet Union, and it was defined by four key features that made the era historically advantageous to American interests. The United States enjoyed unrivaled military primacy, not just globally but within all of the world’s key strategic theaters. Democracy and free markets were ascendant; there were no credible challenges to the liberal ideological model. Great-power conflict had receded to historically low levels with the demise of the Soviet Union. And although international disorder persisted, in the form of humanitarian crises, catastrophic terrorism, and other threats, the major powers were able to achieve remarkably high degrees of cooperation in dealing with that disorder. Today, however, the world has become less benign, as a result of five key trends that are roiling the global system.
First, US primacy has not disappeared, but it has eroded. The US shares of global wealth and military spending have declined — modestly but non-trivially — from their post-Cold War peak, falling, respectively, from over 25 percent and 42 percent in 2004 to around 22 percent and 34 percent in 2015. More important, aggressive challengers—Russia and China in particular—have been steadily developing the military tools needed to prevent the United States from projecting military power into Eastern Europe and East Asia, and to project their own influence farther afield. Military balances in key regions have become far less favorable to Washington and its allies than they were two decades ago; the uncontested primacy of the 1990s has become the highly contested primacy of today.