Transnational Liberalism and U.S. Primacy

The longer U.S. global military primacy endures, the more puzzling it becomes. If, as balance-of-power theory asserts, the international system abhors imbalances of power, why is it tolerating this particular one? How can it be that the unipolar moment is now in its second decade, with few if any concrete signs of decay?

A first step toward understanding the singularity and the causes of U.S. primacy is to note that the United States enjoys being both the only pole in the international system and on the heavy end of an imbalance of world power. In principle, a unipolar international system need not be imbalanced. Neo- realism, the school of thought most concerned with power, implies that a system is unipolar when the second most powerful state cannot by itself counterbalance the most powerful state. For neorealism, only states, not alliances, may be poles. ¹ But in theory a pole may be counterbalanced by an alliance of nonpolar states. Thus U.S. primacy presents two puzzles: the endurance of unipolarity and the endurance of the imbalance of power.

William Wohlforth adequately explains why unipolarity is so durable. The lead of the United States over potential challengers is so great that, barring an unlikely abrupt American collapse, it will take decades for any power to gain polar status. The scale of the imbalance is a product of a number of crucial historical events. The United States became the world's leading economic power in the late nineteenth century; it was compelled by World War II to channel that power into military might; during the Cold War, it continued to amass power to counter its Soviet rival, while potential great powers joined it in counterbalancing; the Soviet Union suddenly disappeared in 1991; and the United States was left as the only pole. If Robert Gilpin and other hegemonic stability theorists are correct, the putative law of uneven growth ensures that unipolarity will erode. ² The erosion may be slow, however.

Wohlforth is less convincing on the persistence of the imbalance of international power or why the American "unipole" still faces no counterbalancing coalition. ³ The United States has the world's largest economy, accounting for 23 percent of gross world product; but the European Union (EU) accounts for 20 percent, China for 12 percent, and Japan for 7 percent. ⁴ The United States has no monopoly on nuclear weapons or offensive delivery systems (although in many areas it enjoys a sizable qualitative advantage). In principle, therefore, a balance of power could emerge were enough states sufficiently motivated to increase their offensive capabilities and form an alliance.

Why is the rest of the world not compelled to counterbalance the United States? ⁵ Wohlforth and Stephen Walt argue that geography inhibits counterbalancing. The country's physical isolation from potential challengers renders it relatively nonthreatening, and any power that counterbalanced the United States would itself be counterbalanced in its own region. ⁶ Other scholars offer institutional, "path-dependent" explanations for continuing U.S. predominance. John Ikenberry argues that the United States and its allies are parties to an implicit constitution that limits U.S. power in exchange for cooperation; moreover, the international institutions that the United States has constructed since World War II pay increasing returns, raising the costs of defection over time. ⁷ Charles Kupchan and Josef Joffe make similar arguments. For Kupchan the United States is a benign unipole that has offered states restraint in exchange for protection. ⁸ For Joffe the United States maintains primacy by following a global Bismarckian strategy, eschewing conquest in favor of making itself indispensable to order in most regions of the world. ⁹

None of these arguments can explain why some states are in fact counterbalancing U.S. might. The explanations commit the fallacy of inferring behavior from outcomes: They assert an absence of counterbalancing from the absence of a balance of international power. Following convention, I define counterbalancing as taking...