"In the twentieth century, no country has influenced international relations as decisively and at the same time as ambivalently as the United States. No society has more firmly insisted on the inadmissibility of intervention in the domestic affairs of other states, or more passionately asserted that its own values were universally applicable. No nation has been more pragmatic in the day-to-day conduct of its diplomacy, or more ideological in the pursuit of its historic moral convictions. No country has been more reluctant to engage itself abroad even while undertaking alliances and commitments of unprecedented reach and scope. The singularities that America has ascribed to itself throughout its history have produced two contradictory attitudes toward foreign policy. The first is that America serves its values best by perfecting democracy at home, thereby acting as a beacon for the rest of mankind; the second, that America’s values impose on it an obligation to crusade for them around the world. Torn between nostalgia for a pristine past and yearning for a perfect future, American thought has oscillated between isolationism and commitment, though, since the end of the Second World War, the realities of interdependence have predominated."