Why the United States Entered World War I

Woodrow Wilson

Three years after the outbreak of World War I, the U.S. declared war on Germany following growing indignation over unrestricted naval warfare.

The United States entered World War One in April 1917. The war began in August 1914 following the assassination of Archduke Francis Ferdinand in Sarajevo, but U.S. President Woodrow Wilson had resisted calls to intervene, basing his 1916 reelection campaign on the slogan, “he kept us out of war.” What events changed American resolve to enter the Great War and, for the first time in the nation’s history, send U.S. troops to fight in the bloody trenches of Europe?

Woodrow Wilson Steers the Nation Away from War

When war erupted in Europe in 1914, President Wilson called upon the nation to respond through neutrality. Wilson was involved with the Congress, attempting to implement progressive reforms. At the same time, the U.S. was responding to civil unrest in Mexico which threatened the nation’s borders and the peace of Central America. Additionally, many Americans were reluctant to enter a war that supported imperialist powers like Britain or autocratic regimes such as Russia.

By April 1917, however, much had changed. Americans were losing their lives on trans-Atlantic carriers and German U-boats relentlessly sunk U.S. ships freighting goods to Britain and France. The May 1915 sinking of the ill-fated Lusitania almost brought the U.S. into the conflict. Germany’s policy of “unrestricted submarine warfare” helped to turn the tide of public opinion against Kaiser Wilhelm and his so-called barbaric atrocities of war.

Changing Conditions in Europe in 1917

In March 1917 the Russian Tsar Nicholas II abdicated, paving the way for a democratic government. Becoming an ally of an autocratic dynasty was no longer an ideological problem for Americans. Perhaps Woodrow Wilson was correct: U.S. intervention would help to make the world “safe for democracy.”

In Europe, 1917 began as the crucial year for both the Allies and Imperial Germany. Three years of war had lowered morale. Supplies were depleted and anti-government groups like the Socialists were clamoring for immediate change. In the final months before armistice, Russia experienced the October revolution bringing Lenin to power while in Germany riots, including a naval mutiny, forced the Kaiser out of the country.

But as 1917 began, these events had not yet occurred and both sides believed that victory was still possible. Early in 1917 President Wilson was presented with the Zimmermann Telegram, intercepted by the British. The document disclosed German overtures to Mexico, promising a return of lost territory that dated to the Mexican cession of 1848, in return for a war declaration against the U.S. Germany gambled dangerously, attempting to keep America out of the conflict.

The German Gamble Results in a U.S. War Declaration

At the same time, the German gamble included a resumption of unrestricted naval warfare. U.S. ships were sent to the bottom by U-boats without prior warning. In Europe, the Allies depended upon every convoy bound for their ports to break the stalemate of trench warfare. Wilson felt compelled to ask Congress for a war declaration, confident that American outrage over Germany’s actions would support U.S. participation.

Another argument for U.S. entry into the Great War involves the massive debt owed to U.S. banks and businesses. This argument played a role in the 1940’s as another Congress attempted to curtail U.S. funding for the Allied cause against Nazi Germany.

Following congressional approval, the Wilson administration embarked upon a massive nation-wide propaganda campaign to marginalize criticisms and bolster support for the war effort. The United States entered World War One for a number of reasons that included Wilson’s idealism regarding global peace and democracy, the German policy of unrestricted naval warfare, and growing indignation among Americans with events in Europe that threatened U.S. future interests.


  1. Leon H. Canfield, The Presidency of Woodrow Wilson: Prelude to a World in Crisis (Fairleigh Dickinsen University Press, 1966)
  2. David Fromkin, Europe’s Last Summer: Who Started The Great War In 1914? (Alfred A. Knopf, 2004)
  3. Page Smith, America Enters The World: A People’s History Of The Progressive Era And World War I, Volume Seven (McGraw-Hill Book Company, 1985)