Despite the development of a consensus foreign policy during the early years of the Cold War that supported containment of the Soviet Union, there were both internationalists and pacifists who opposed the efforts of the Truman administration. These groups felt that American actions, including the Truman Doctrine, the Marshall Plan, the North Atlantic Treaty, and even the Korean War weakened the UN, threatened the Soviet Union with war, hindered European economic recovery, and promoted colonialism. Often mislabeled as isolationists, both the pacifists, with their traditional opposition to war, and the liberal internationalists, who supported efforts to continue the wartime alliance with the Soviets through the development of a strong UN, felt that the United States should play an active role in world affairs.

The peace movement forces have been marginalized or dismissed as insignificant by many historians, however, while their impact was minimal in the late 1940s and early 1950s, their ideas would later re-emerge to have a strong impact on American policy, particularly in the ban the bomb and the antiwar movements of the Vietnam era. They continued to support efforts to maintain the Soviet alliance through the UN, to assist in the reconstruction of the world economy, to promote disarmament, and to end colonialism. While a commitment to these ideas would probably not have prevented the Cold War, it might have lessened its severity or slowed the arms race between the United States and the Soviet Union.