The United States Enters World War I
Wilson takes the country into a European war to "make the world safe for democracy"
Quick facts
- War message
- April 2, 1917, by Woodrow Wilson
- War declared
- April 6, 1917, against Germany
- Triggers
- Unrestricted submarine warfare, the Zimmermann Telegram
- Wilson's aim
- To "make the world safe for democracy"
What happened
The United States stayed out of World War I for its first two and a half years, and Woodrow Wilson won reelection in 1916 partly on having kept the country out. Two German actions changed that. Germany resumed unrestricted submarine warfare in early 1917, sinking merchant and passenger ships, and the intercepted Zimmermann Telegram revealed a German offer to help Mexico recover territory it had lost to the United States. On April 2, 1917, Wilson went before a joint session of Congress to ask for a declaration of war, arguing that the world must be made safe for democracy. Congress voted for war, and the declaration against Germany was final on April 6, 1917. American troops began reaching Europe in numbers in 1918.
Why it matters
Entry into World War I marked the United States stepping onto the world stage as a decisive military power, and the fresh American forces helped tip the balance toward Allied victory in 1918. Wilson's vision of a postwar order built on democracy and a League of Nations shaped, and then frustrated, American foreign policy, and the war's disappointments fed the isolationism of the 1920s and 1930s.
How we know
Wilson's war message survives in the National Archives, along with the congressional declaration of war, and the causes including submarine warfare and the Zimmermann Telegram are documented in State Department and diplomatic records.
Sources
- National Archives. President Wilson's Address to Congress Leading to a Declaration of War Against Germany (1917) · Primary source (author-declared)archives.gov · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- Office of the Historian, U.S. Department of State. American Entry into World War I, 1917 · Reputable sourcehistory.state.gov · The domain "history.state.gov" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- World War I → · This is the American entry into World War I; see the World War I timeline for the war's origins, the Western Front, and the 1918 armistice.