When the USA declared war in April 1917, Wilson sent the American Expeditionary Force (AEF) under the command of General John Pershing to the Western Front. By May 1918, there were over 500,000 US soldiers in France.

By July 1918 there were over a million US soldiers in France. General John Pershing deployed US troops to help the French defend the Western Front during the Aisne Offensive in May and at the Marne in June. US troops also took part in the Allied attacks at Le Hamel and Canal du Nord before Pershing launched his own offensive at St Mihiel (September) and Meuse-Argonne (October).

More than 2 million troops eventually reached Europe but a large number arrived too late to see any action. The American Expeditionary Force suffered 264,000 casualties, including 50,554 killed in battle and about 25,000 by disease. About 200,000 Afro-Americans served in the US Army in Europe, but only 42,000 were classified as combat troops. Completely segregated, they fought with the French Army during the war.