We tend to assume that power, like nature, abhors a vacuum. In the history of world politics, it seems, someone is always the hegemon, or bidding to become it. Today, it is the United States; a century ago, it was the United Kingdom. Before that, it was France, Spain, and so on. The famed 19th-century German historian Leopold von Ranke, doyen of the study of statecraft, portrayed modern European history as an incessant struggle for mastery, in which a balance of power was possible only through recurrent conflict.

The influence of economics on the study of diplomacy only seems to confirm the notion that history is a competition between rival powers. In his bestselling 1987 work, The Rise and Fall of the Great Powers: Economic Change and Military Conflict from 1500 to 2000, Yale University historian Paul Kennedy concluded that, like all past empires, the U.S. and Russian superpowers would inevitably succumb to overstretch. But their place would soon be usurped, Kennedy argued, by the rising powers of China and Japan, both still unencumbered by the dead weight of imperial military commitments.

In his 2001 book, The Tragedy of Great Power Politics, University of Chicago political scientist John J. Mearsheimer updates Kennedy's account. Having failed to succumb to overstretch, and after surviving the German and Japanese challenges, he argues, the United States must now brace for the ascent of new rivals. “[A] rising China is the most dangerous potential threat to the United States in the early twenty-first century,” contends Mearsheimer. “[T]he United States has a profound interest in seeing Chinese economic growth slow considerably in the years ahead.” China is not the only threat Mearsheimer foresees. The European Union (EU) too has the potential to become “a formidable rival.”...