When Did the U.S. Join World War I?

The United States entered World War I on April 6, 1917, joining the Allied Powers of Great Britain, France, Italy and Russia in the fight against the Central Powers of Germany, the Austrian-Hungarian Empire, the Ottoman Empire, and Bulgaria. Over 2 million Americans fought in World War I.

World War I consisted primarily of trench warfare, with opponents digging series of trenches on the battlefield in an effort to move troops without exposing them to machine gun fire on open ground. The machine gun was just one of the many innovations brought to the battlefield in World War I, along with modern artillery, airplanes, submarines and gas warfare.