When did the u. s. a. join world war one?
April 6th, 1917
The United States declared war on Germany, thereby formally entering World War I, on April 6, 1917. The American Expeditionary Forces, known as the AEF, was established in France by President Woodrow Wilson on July 5, 1917 but did not participate in combat until October 21, 1917.
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