In World War II, Americans realized they could not wish or will away the implications and complications of power. As one leader of Senate Republicans and a former critic of international commitments put it, after Pearl Harbor "isolationism was dead for any realist." Autocrats in Europe and Asia threatened U.S. security in a drastic revival of the power problem. Americans had to face both the necessity and the consequences of force and violence in international affairs. Even such an idealist as Secretary of State Cordell Hull was led to believe that only total victory based on unconditional surrender would bring total peace. The greatest debates in the United States in the late months of the war focused less on the iniquity of force than on the question of who was a friend and who an enemy.
At war's end some Americans tried to grasp a second chance to internationalize their power problem and the specter of force. They believed or hoped that international organization might provide a solution to the power problem and a way to avoid perpetually violent international politics through collective security and peacekeeping. At the same time, other Americans, less confident in the future of international politics, favored unilateralism and national security based on America's unparalleled economic and military power. They relied especially on the newfound power of the atomic bomb as the ultimate or absolute weapon. What Harry Truman called America's "sacred trust" would not be shared with the world or with the new international peacekeeping body until such time that Americans could be sure that there could be no abuse of this awesome power.
After the demonstrated weakness of the United Nations, which proved incapable of subordinating great-power conflicts of interest or of assuming responsibility for control of atomic technology and weapons, international idealism was supplanted in 1947 by a determined application of American power and force in every form and in virtually every forum. What was dubbed the Truman Doctrine committed American might to the containment of communism in whatever form, be it internal subversion or external aggression. However, in a larger sense, American leaders in the years following World War II redefined the idea of national security. The goal of this new postwar or Cold War policy was to establish and maintain a preponderance of American power throughout the world. This globalist approach to world affairs involved both military alliances such as the North Atlantic Treaty Organization (NATO) and massive economic programs such as the Marshall Plan. Although sometimes collective, these commitments were predicated on U.S. military and economic power. Looking back on this period, Truman's secretary of state, Dean Acheson, aptly described it as the "creation" of modern American foreign relations.
After World War II, Americans accommodated themselves to the possession and exercise of economic power and military force on an unprecedented scale and sought new answers to the perennial problems of power. The various forms of traditional unilateralism—nonentanglement, neutrality, isolationism—gave way to a new structure of American globalism. Most important, Americans became reconciled to the use of force to such an extent that they entered a new era of interventionism that, with the Cold War, resulted in a huge standing military establishment.