America emerged from World War II as the world's greatest power, economically, politically, and in some respects even militarily despite almost immediate demobilization. Unlike its major allies, Britain, France, and the Soviet Union, it suffered virtually no damage at all besides its comparatively small losses in manpower. Its strength, however, imposed on the country the burden of enormous responsibilities that were quickly put to the test, responsibilities that most Americans resented and resisted. It took extraordinary leadership at the top to move U.S. policy into line with its responsibilities as a major international power.

Unlike the aftermath of World War I, the second postwar era proved to be one of those rare and wonderful moments in history when a policy-making elite moved with foresight and dispatch to meet impending human and political disaster, even, it must be said, in the face of considerable popular domestic resistance.

In the environment of the war, liberal internationalism had risen triumphant over the nation's long-standing tradition of unilateral nationalism. Not long after the U.S. entry into the war, it became conventional wisdom that America's unwillingness to take on a leadership role after the First World War and in the 1930s had contributed in major ways to both the Depression and the ascendancy of world fascism.