The tradition of nonentanglement with the affairs of Europe and other countries found a new name in the interwar years: isolationism. The U.S. Senate rejected President Wilson's vision of an international organization, the League of Nations, committed to maintaining world peace through arbitration of conflict and mutual respect of the independence and territorial integrity of all member states. Isolationists believed the United States should not be under obligation to any other nation. As Jefferson, Washington, and others had observed, the United States was uniquely blessed with geographic isolation from the degeneracy of the Old World. With friendly, unthreatening neighbors at its northern and southern borders and vast oceans to the east and west, the United States had little to fear from foreign attack. Why should it jeopardize this exceptional degree of peace and security by involving itself with the affairs of others? Wilson's successor, President Warren G. Harding, made clear in his Inaugural Address (March 1921) that "Confident of our ability to work out our own destiny, and jealously guarding our right to do so, we seek no part in directing the destinies of the Old World. We do not mean to be entangled."
Harding and others did not believe that the United States should have no contact whatsoever with the outside world, but that it should remain aloof from the petty squabbles and adversarial alliances common in Europe while maintaining its traditional interests within its own hemisphere. It would seek to return to the role of having nothing but peaceful relations with others and to present an exemplary nation to which the rest of the world could aspire. The isolationists used language and arguments that were consistent with the exemplar strand of the belief in American exceptionalism.
The two strands of exceptionalism, however, again came into conflict during the interwar period. A major public debate took place between the isolationists and the "internationalists" who believed the United States had a duty to intervene in world affairs. When Britain and France declared war on Germany in September 1939, President Franklin Delano Roosevelt, as expected, declared U.S. neutrality. The isolationist impulse found enough popular approval to cause the Roosevelt administration to seek ways of assisting Britain and France short of intervening directly in the war. But this final popular attachment to isolationism was shattered by the surprise Japanese attack on the U.S. naval base at Pearl Harbor, Hawaii, and other American bases in the Pacific on 7 December 1941. The reality of a devastating military strike on American territory silenced isolationist claims. The threat posed by Germany and Japan was obvious enough to enable the public to base their support for joining the war on political and strategic reasoning, at least after Pearl Harbor. Yet Roosevelt still felt the need to employ exceptionalist rhetoric to justify American intervention. In his fireside chat to the nation following the Japanese attack, he assured the American people that "When we resort to force, as now we must, we are determined that this force shall be directed toward ultimate good as well as against immediate evil. We Americans are not destroyers—we are builders."
In January 1942, Roosevelt declared that American victory in the war would be a "victory for freedom." He made clear that a central U.S. war objective was to establish and secure "freedom of speech, freedom of religion, freedom from want, and freedom from fear everywhere in the world." The "Four Freedoms" rooted the war effort in one of the central ideas of American political culture. The contrast between freedom and fascism was a central metaphor in American public discourse and official rhetoric throughout the war. Even before the United States entered the war, the Atlantic Charter (August 1941) had indicated that Roosevelt believed the United States must assume global responsibilities after Germany and Japan were defeated. To win the war would not be enough. An allied victory must lead to lasting peace and security in the world based upon universal values and principles traditionally espoused by Americans. To lead such a future was an American responsibility and duty that would not only promote U.S. interests but also those of all humankind. Roosevelt acknowledged that American power in itself brought responsibility, but he also invoked the providential idea that it was God's will. In his final inaugural address (20 January 1945), he claimed that God "has given to our country a faith which has become the hope of all peoples in an anguished world."
No matter how convincing the strategic or other tangible reasons for U.S. intervention in World War II, Roosevelt, like presidents before him, couched his justifications in terms consistent with the belief in the exceptional nature of the United States. That he did so when American security was so clearly threatened is substantial evidence that exceptionalism frames the discourse of U.S. foreign policymaking.