After World War I, debate in the United States over the use of force in pursuit of national goals continued. What has been misleadingly called a period of isolation did not witness an American withdrawal from world power, only from an active leadership role in world politics. Americans in the 1920s pointed to the perversity of war and the perversion of the peace to prove that power—power politics, the old politics of Europe—was still corrupt and corrupting. They did not refuse to recognize that their country was powerful, but they proposed a narrower definition of the national interest than that proposed by Wilson. They also advocated restraint in the use of force and a partial withdrawal, at least at the political and diplomatic level, from the complicated and uncontrollable world arena. In opposition, other Americans, imbued with what was described as Wilsonian or liberal idealism, held out the prospect of harmonious, just, lawful international relations, dependent on the determination of upright men and a policing of the international community by moral nations—forcibly, if necessary.
For the ensuing interwar period the polarization of opinion on the proper uses of American power defined the limits of the nation's diplomacy. Chastened by the experience of the world war, Americans were uncomfortable with the use of force and determined not to employ it except within the Western Hemisphere. Even there, American policy was noticeably uncertain; the days of repeated and prolonged military intervention slowly but surely came to an end. What emerged came to be known under Franklin Roosevelt as the Good Neighbor Policy, a shift from the use of military force to reliance on economic hegemony to lead hemispheric affairs in a direction consistent with U.S. national interests. But even earlier, in the 1920s, American foreign policy had turned once more to economics as an alternative to the politics of force; not to coercive economic diplomacy but to defensive diplomacy, the conservative economics of protection, sound money, and relatively equal treatment for all comers to the American marketplace. This was policy until the Great Depression overturned the conventional wisdom of economics and diplomacy and forced politicians to use untried and previously unimaginable expedients.
In one sense the limits on power imposed by divisions of opinion in the 1920s and 1930s proved a liability for policy and leadership, or so it seemed in retrospect. The same doubts about the uses of power and force that caused Americans to terminate interventions in Latin America later caused them to hesitate, equivocate, and delay too long in dealing with the aggressive European and Asian autocracies of the 1930s.
At the same time Adolf Hitler came to power in Germany, President Franklin D. Roosevelt, having learned the lesson of Woodrow Wilson's failure in forging too far ahead of public and congressional opinion, focused on anti-Depression New Deal policies as the international system forged at Versailles began to come apart in Asia and Europe. Having tacitly endorsed the popular policy of appeasement as late as the 1938 Munich Conference, Roosevelt aligned U.S. economic power with the anti-Axis Allies after the outbreak of war in 1939, declaring that America would act as the "arsenal of democracy." That policy of supplying both the British and later the Soviet Union with American-made arms and other matériel led by late 1941 to an undeclared naval war in the North Atlantic. In Asia and the Pacific, Roosevelt's increasingly determined opposition to Japanese expansion included a show of force in the form of forward basing of American naval and air power and ever-tightening economic sanctions aimed at forcing Japan into abandoning its imperial aims. In what was perhaps the first test of the lessons of Munich, Japan responded by attacking the U.S. Pacific fleet at Pearl Harbor. In the end, the American dilemma of whether and how to use its power finally was settled not by Americans but by the course of events—that is, by the power and politics of Europe and Asia.