U.S. Involvement in the War

When the war began in 1939, the United States declared its neutrality. Although isolationist feeling remained strong, many Americans, including President Franklin Delano Roosevelt, sympathized with those who battled the Axis powers. In time, Roosevelt found ways around the Neutrality Acts to provide aid, including for Britain, as it stood alone against Hitler.

Roosevelt Supports the Allies

In March 1941, FDR persuaded Congress to pass the Lend-Lease Act. It allowed him to sell or lend war materials to “any country whose defense the President deems vital to the defense of the United States.” The United States, said Roosevelt, would not be drawn into the war, but it would become “the arsenal of democracy,” supplying arms to those who were fighting for freedom.

To show further support, Roosevelt met secretly with Churchill on a warship in the Atlantic in August 1941. The two leaders issued the Atlantic Charter, which set goals for the war—“the final destruction of the Nazi tyranny”—and for the postwar world. They pledged to support “the right of all peoples to choose the form of government under which they will live” and called for a “permanent system of general security.”

Growing Tensions with Japan

Although Roosevelt viewed Hitler as the greatest menace to world peace, it was tensions with Japan that finally brought the United States into the war. The United States held several possessions in the Pacific, including the Philippines and Hawaii.

When war broke out in Europe in 1939, the Japanese saw a chance to grab European possessions in Southeast Asia. Japanese forces took control across Asia and the Pacific. Japan claimed that its mission was to help Asians escape Western colonial rule. In fact, the real goal was a Japanese empire in Asia. The rich resources of the region, including oil, rubber, and tin, would be of immense value in fighting Japan's war against the Chinese.

A map shows Axis advances in 1941.
Image Long Description

The Soviet Union joined the Allies after Germany's invasion.

Analyze Maps

How might this new enemy affect Germany's war effort in geographic terms?

In 1940, with Europeans distracted by war, Japan advanced into French Indochina and the Dutch East Indies. In response, the United States banned the sale of war materials, such as iron, steel, and oil, to Japan. Japanese leaders saw this move as a threat to Japan's economy and its Asian sphere of influence.

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Table of Contents

World History Topic 1 Origins of Civilization (Prehistory–300 B.C.) Topic 2 The Ancient Middle East and Egypt (3200 B.C.–500 B.C.) Topic 3 Ancient India and China (2600 B.C.–A.D. 550) Topic 4 The Americas (Prehistory–A.D. 1570) Topic 5 Ancient Greece (1750 B.C.–133 B.C.) Topic 6 Ancient Rome and the Origins of Christianity (509 B.C.-A.D. 476) Topic 7 Medieval Christian Europe (330–1450) Topic 8 The Muslim World and Africa (730 B.C.-A.D. 1500) Topic 9 Civilizations of Asia (500–1650) Topic 10 The Renaissance and Reformation (1300–1650) Topic 11 New Global Connections (1415–1796) Topic 12 Absolutism and Revolution Topic 13 The Industrial Revolution Topic 14 Nationalism and the Spread of Democracy (1790–1914) Topic 15 The Age of Imperialism (1800–1914) Topic 16 World War I and the Russian Revolution (1914–1924) Topic 17 The World Between the Wars (1910–1939) Topic 18 World War II (1930–1945) Topic 19 The Cold War Era (1945–1991) Topic 20 New Nations Emerge (1945–Present) Topic 21 The World Today (1980-Present) United States Constitution Primary Sources 21st Century Skills Atlas Glossary Index Acknowledgments