Power Down

A history of United States ­hegemony — a term that international relations scholars use to describe consent-based world leadership — is a chronicle of a decline foretold. Consider the original Sputnik moment, in 1957; the breakup of the Bretton Woods system, in the early 1970s; the ignominious withdrawal from Vietnam, in 1975; and all those anxieties about an “emerging Japanese superstate” and “imperial overstretch.” Predictions of a “post-American world” have suffered few shortages, even as the United States has actually gone from strength to strength. The “unipolar moment” that followed the fall of the Berlin Wall certainly halted the prognostications of declinism, but only for a while.

In December 2004, amid daily footage of American soldiers fighting and dying in the streets of Fallujah, the U.S. federal government’s own National Intelligence Council foresaw “the rise of new powers, new challenges to governance, and a more pervasive sense of insecurity” by 2020...