Despite increasing reliance on foreign trade as a pillar of the U.S. economy, the United States sought to limit its global responsibilities in the aftermath of World War I. The Senate's rejection of the Versailles Treaty meant that the United States would not join the League of Nations despite the fact that it was primarily the creation of President Woodrow Wilson.
Instead, the United States pursued a policy of independent internationalism during the 1920s, promoting naval disarmament at the Washington Conference in 1921–22; establishing a "reparations triangle," which established a relationship between German reparations payments to the Allies and Allied war debt payments to the United States through the Dawes and Young Plans (1924 and 1929, respectively); and intervening in Central America and the Caribbean throughout the decade.
The onset of the Great Depression began to reverse this internationalism. During the latter stages of the Hoover administration and the most of the first two terms of the Franklin D. Roosevelt administration, isolationist sentiment grew in Congress and in the country.
This desire to limit involvement in the growing conflicts found in Europe and Asia in the mid-1930s became public policy through the creation of the Neutrality Acts of 1935, 1936, and 1937. The Neutrality Act of 1935 forbade arms sales to belligerents during a recognized state of war. The Neutrality Act of 1936 renewed the 1935 provision and added a commitment to stay out of the ongoing Spanish civil war while also forbidding loans by banks to belligerents.
The Neutrality Act of 1937 added to the first two provisions that forbade citizens from traveling on belligerents' vessels and limited trade in nonmilitary goods with belligerents to a "cash-and-carry" basis, meaning that belligerents could purchase nonmilitary items from the United States with cash only and would have to pick up the goods from the United States in their own ships.
These three acts limited presidential control of foreign policy by eliminating any distinction between aggressors and victims in a conflict, eliminating a key moral component from U.S. policy. That these acts had very little relationship to the actual events in Europe and Asia troubled the isolationists not at all. Their goal was to keep the United States out of the growing conflicts in the rest of the world.
The Roosevelt administration's acquiescence in the creation of these acts reflected the president's emphasis on dealing with the Great Depression. The primary movers behind the Neutrality Acts tended to support the New Deal.
As events in Europe and Asia pushed the world once again toward war, Roosevelt began to take tentative steps toward challenging isolationist dominance. On October 5, 1937, he spoke to a nationwide audience from the isolationist stronghold of Chicago. In the speech he called for the quarantine of aggressor nations by the world's peace-loving peoples.
However, when the British sought clarification on what Roosevelt intended to do to carry out this quarantine, the president responded that both U.S. public opinion and the Neutrality Acts precluded any actual preemptive actions by the president. Roosevelt all but repudiated the speech over the next several weeks.
One of the primary consequences of U.S. isolationism was the enhanced commitment of Britain and France to a policy of appeasement. If they could not count on the United States for loans, guns, or assistance, the British and French did not believe they could credibly resist Germany militarily.
Hence, they were willing to trade land for peace, acquiescing in the Anschluss (unification) of Germany and Austria in March 1938. After a summer of crisis created by Adolf Hitler's demand for autonomy for ethnic Germans living in the Sudetenland in Czechoslovakia, the British and French pressured the Czech government to meet the demand.
When Hitler responded by changing the demand to German annexation of the territory, the British and French at first reluctantly mobilized their militaries but then agreed to meet with Hitler and Italian dictator Benito Mussolini at Munich, where the Czechs were forced to cede the territory to Germany.
During the intervening year, Roosevelt slowly and tentatively began to challenge isolationist dominance, specifically requesting a liberalization of the Neutrality Acts' limitation on arms sales in his State of the Union message on January 4, 1939.
Building on the anti-German outcry over the Kristallnacht attacks on German Jews on November 10, 1938, Roosevelt began to salt his discussions with congressional leaders and the press with references to the growing danger of Germany, a danger confirmed by its seizure of the remainder of Czechoslovakia on March 15, 1939. This aggression ended the policy of appeasement by Britain and France and seemed to strengthen Roosevelt's hand in demanding Neutrality Act revision.
When the war began with the German invasion of Poland on September 1, 1939, followed by the French and British declarations of war two days later, Roosevelt seized the opportunity to act. After issuing a neutrality proclamation in which he clearly was not calling for an absolutely neutral stance toward the belligerents in Europe, Roosevelt called Congress back into session to again take up the issue of revising the Neutrality Acts.
Despite fierce resistance from the isolationists, the arms embargo was lifted. However, the isolationists did force a cash-and-carry provision into the act for the sale of arms and munitions.
Through 1940 and especially after the fall of France in June, isolationists hammered away at the sale of arms to the British, calling for arms to be used to defend the United States instead. Led by the organization America First, the isolationists predicted Britain's defeat and criticized Roosevelt for wasting U.S. resources on a lost cause.
The most formidable spokesman for America First was aviation hero Charles Lindbergh, who argued that the Germans were far superior to the British in air power and that this would inevitably lead to Britain's defeat.
Nevertheless, Roosevelt not only continued to sell increasing amounts of arms to the British, he also authorized a trade of 50 U.S. destroyers to Britain in return for the right to lease nine British bases in the Western Hemisphere. The destroyers would both help the British convoy goods across the Atlantic and serve as morale-boosting evidence of the U.S. potential to assist.
Ironically, while isolationists condemned Roosevelt's behavior in the Atlantic as designed to trigger U.S. entry into the war, it would be events in Asia that would actually bring about the end to neutrality and isolationism. U.S. economic sanctions against Japan over the seizure of French Indochina, particularly an embargo on the sale of oil, led to tense negotiations between the two sides.
Ultimately, the negotiations failed because of incompatible goals; the United States demanded Japanese withdrawal from Indochina and China in return for normalizing trade, while the Japanese demanded that the United States recognize the new territorial arrangements in Asia and resume normal trade. As the talks broke down, the Japanese government implemented the plan of Admiral Isoroku Yamamoto to launch a surprise attack on the American Pacific Fleet at anchor at Pearl Harbor, Hawaii.
By attacking the United States in this manner, the Japanese accomplished something Roosevelt had failed to do for the previous two years: unite the people of the United States behind intervention in the war while mortally wounding isolationism in the United States. On December 8, 1941, Congress approved a declaration of war against Japan, with only one member dissenting. Isolationism was discredited, and the United States united behind the war effort.