Those who believe Europe is weak, ineffectual and sclerotic are wrong. Europe might look frail and feeble against American military might, but that expression of power is shallow and narrow. Or so says Mark Leonard, one of Europe's brightest new policy thinkers, in a book sure to stir and provoke his American contemporaries. America's centralized, militarized supremacy, he argues, has become so overwhelming that it has defeated everything, including itself. It's capable of imposing itself anywhere but when its back is turned its potency wanes. Europe's reach, by contrast, is broad and deep,...