The United States Enters the War

Soon after the Russian Revolution began, another event altered the balance of forces. The United States declared war on Germany. Many factors contributed to the decision of the United States to exchange neutrality for war in 1917.

Unrestricted Submarine Warfare

A major reason for the U.S. entry into the war was German submarine attacks. After the sinking of the Lusitania and under pressure from President Wilson, Germany had agreed to restrict its submarine campaign. By early 1917, however, Germany was desperate to break the stalemate in the war. On February 1, the German government announced that it would resume unrestricted submarine warfare. Wilson angrily denounced Germany.

Photo of a trench, where guns lean against the sides as men sleep and eat in holes.

Soldiers ate, slept, fought and died in the trenches. As the war dragged on and casualties mounted, morale was severely tested.

Anti-German Sentiment Grows

Many Americans supported the Allies because of cultural ties. The United States shared a cultural history and language with Britain and sympathized with France as another democracy. On the other hand, some German Americans favored the Central Powers. So did many Irish Americans, who resented British rule of Ireland, and Russian Jewish immigrants, who did not want to be allied with the tsar. The resumption of unrestricted submarine warfare, however, increased anger toward Germany and spurred support for the Allies.

Another German move also angered Americans. In early 1917, the British intercepted a message from the German foreign minister, Arthur Zimmermann, to his ambassador in Mexico. In the note, Zimmerman wrote that if Mexico joined Germany in the event of war with the United States, Germany would help Mexico “to reconquer the lost territory in New Mexico, Texas, and Arizona.” Britain revealed the Zimmermann note to the American government. When the note became public, anti-German feeling intensified in the United States.

Cartoon of a man seated at a desk reading a long scroll titled Germany’s reply, with another man in a long beard looking over the seated man’s shoulder, next to a trash basket over flowing with paper.

Germany resumed unrestricted submarine warfare in 1917. Here, President Wilson reads a German message and ponders what to do.

Analyze Political Cartoons

What does the overflowing waste basket suggest?

Wilson Asks for a “War to End War”

In April 1917, Wilson asked Congress to declare war on Germany. “We have no selfish ends to serve,” he stated. Instead, he painted the conflict idealistically as a war “to make the world safe for democracy” and later as a “war to end war.”


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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