7.3 U.S. Entry into World War II

World War II reshaped America's role on the global stage. As fascist regimes in Europe and Asia threatened world peace, the U.S. shifted from isolationism to interventionism, providing crucial support to Allied nations.

The Japanese attack on Pearl Harbor in 1941 catapulted the U.S. into the war. This pivotal event united Americans behind the war effort, transforming the nation's economy and society to meet the demands of a global conflict.

U.S. Involvement in World War II

Rising Tensions and Aggressive Expansionism

• Fascist regimes emerged in Germany, Italy, and Japan during the 1930s heightened international tensions
• These regimes pursued aggressive expansionist policies challenged the post-World War I international order
  • Japanese invasion of Manchuria (1931)
  • German annexation of Austria and the Sudetenland (1938)
• German invasion of Poland in September 1939 triggered the outbreak of World War II in Europe prompted a reevaluation of U.S. foreign policy

U.S. Policy Shift from Isolationism to Interventionism

• Initially, the U.S. pursued a policy of isolationism aimed at preventing American involvement in foreign conflicts
  • Neutrality Acts of the 1930s exemplified this approach
• President Franklin D. Roosevelt's "Quarantine Speech" (1937) signaled a shift towards confronting aggressor nations, although the U.S. remained officially neutral
• Fall of France (June 1940) and the Battle of Britain heightened concerns about the spread of fascism and the potential threat to U.S. security
• Selective Training and Service Act (1940), the first peacetime draft in U.S. history, demonstrated growing preparedness for possible involvement in the war

Pearl Harbor's Impact

Surprise Attack and Shift in Public Opinion

• Japanese launched a surprise attack on the U.S. naval base at Pearl Harbor, Hawaii (December 7, 1941)
  • Killed over 2,400 Americans and destroyed numerous ships and aircraft
• The attack dramatically shifted American public opinion from isolationism to support for entering the war
  • Congress overwhelmingly approved President Roosevelt's request for a declaration of war against Japan
• President Roosevelt's "date which will live in infamy" speech (December 8, 1941) emphasized the need for the U.S. to defend itself and its allies against Axis aggression

U.S. Entry into World War II

• Germany and Italy, as allies of Japan, declared war on the United States (December 11, 1941) effectively bringing the U.S. into a two-front war in Europe and the Pacific
• The attack led to a significant expansion of the U.S. military with millions of Americans enlisting or being drafted into service
• The U.S. government implemented wartime measures in response to heightened national security concerns
  • Rationing
  • Increased industrial production
  • Internment of Japanese Americans

U.S. Response to World War II

Initial Neutrality and Support for Allies

• The U.S. government initially maintained a policy of neutrality following the outbreak of war in Europe as dictated by the Neutrality Acts of the 1930s
• President Roosevelt and his administration sought ways to support Allied nations, particularly Great Britain, without directly entering the war
  • "Cash and carry" policy allowed Allied nations to purchase U.S. goods if they transported them in their own ships
  • "Destroyers for Bases" agreement (1940) exchanged American destroyers for British naval bases
• The Atlantic Charter (August 1941), signed by President Roosevelt and British Prime Minister Winston Churchill, outlined Allied goals for the post-war world signaled growing U.S. support for the Allied cause

Economic Sanctions and Escalating Tensions with Japan

• The U.S. government responded to Japanese aggression in Asia by imposing economic sanctions
  • Export Control Act (1940) restricted the sale of strategic materials to Japan
• In 1941, the U.S. government froze Japanese assets in the United States and imposed an oil embargo on Japan in response to its occupation of French Indochina further escalating tensions between the two nations

Lend-Lease Act Significance

Military Aid to Allied Nations

• The Lend-Lease Act (March 1941) allowed the U.S. to provide military equipment and supplies to Allied nations without requiring immediate payment effectively ending the U.S. policy of neutrality
• Lend-Lease aid was crucial in supporting the British war effort, particularly in the Battle of the Atlantic
  • U.S. ships and supplies helped counter German U-boat attacks on Allied shipping
• The extension of Lend-Lease aid to the Soviet Union after the German invasion (June 1941) helped bolster Soviet resistance against Nazi Germany on the Eastern Front

Growing U.S. Commitment to the Allied Cause

• The Lend-Lease Act demonstrated the U.S. government's growing commitment to the Allied cause and its willingness to take on a more active role in the war effort, even before formally entering the conflict
• Other forms of pre-war assistance, such as the "cash and carry" policy and the "Destroyers for Bases" agreement with Great Britain, helped lay the groundwork for U.S. entry into World War II
• The provision of pre-war assistance to Allied nations contributed to the formation of the Allied coalition that ultimately defeated the Axis powers