Over the next two decades, international politics will be shaped by whether the international system remains unipolar or is transformed into a multipolar system. Can the United States sustain its primacy? Or will the emergence of new great powers reorder the distribution of power in the international system? If U.S. power is waning, will power transition dynamics result in security competitions and an increased possibility of war? In particular, what are the implications of China's rapid ascent to great power status? If the United States is unable to preserve its hegemonic role, what will happen to the security and economic frameworks that it took the lead in creating after the end of World War II and that have provided the foundation for the international order ever since? In a world no longer defined by U.S. hegemony, what would become of globalization and the open international economic system that the United established after World War II and expanded after the Cold War ended? This essay reviews five publications that grapple with these questions: Stephen G. Brooks and William C. Wohlforth, World Out of Balance: International Relations and the Challenge of American Primacy ; Parag Khanna, The Second World: Empires and Influence in the New Global Order ; Kishore Mahbubani, The New Asian Hemisphere: The Irresistible Shift of Global Power to the East ; National Intelligence Council, Global Trends 2025: A Transformed World ; and Fareed Zakaria, The Post-American World .

The conventional wisdom among U.S. grand strategists is that U.S. hegemony is exceptional—that the United States need not worry about other states engaging in counterhegemonic balancing against it. The case for U.S. hegemonic exceptionalism, however, is weak. Contrary to the predictions of Waltzian balance of power theorists, no new great powers have emerged since the end of the Cold War to restore equilibrium to the balance of power by engaging in hard balancing against the United States—that is, at least, not yet. This has led primacists to conclude that there has been no balancing against the United States. Here, however, they conflate the absence of a new distribution of power in the international political system with the absence of balancing behavior by the major second-tier powers. Moreover, the primacists' focus on the failure of new great powers to emerge, and the absence of traditional “hard” (i.e., military) counterbalancing, distracts attention from other forms of counterbalancing—notably “leash-slipping”—by major second-tier states that ultimately could lead to the same result: the end of unipolarity. Because unipolarity is the foundation of U.S. hegemony, if it ends, so too will U.S. primacy.