The U.S. in World War I

Updated February 21, 2017 | Factmonster Staff

1914-18 (U.S. involved, 1917-18)


America's Role in WWI: A Video


Watch this video about America's delayed entry in WWI. See the role of submarine warfare, President Wilson, and the Allied cause.

“The world must be made safe for democracy.”—President Woodrow Wilson, World War I

WWI Facts

  • U.S. troops engaged: 4,734,991
  • American casualties: 53,402
  • The U.S. joined the Allies (Britain, France, Russia, Italy, and Japan), who were at war with the Central Powers (Germany, Austria-Hungary, and Turkey), after German submarines began sinking unarmed ships—notably the Lusitania.
  • The U.S. declared war on Germany April 6, 1917, and submarine warfare reached its peak in the North Atlantic Ocean.
  • American troops landed in France and held off a German offensive in Château-Thierry.
  • French and American troops stopped a critical German attack just outside of Paris in July and August of 1918. A counterattack was ordered and, with the help of the British, the Allies forced Germany back to where its attack began—the Hindenburg Line.
  • World War I was characterized by trench warfare. Each army dug protective trenches-long, deep rows of ditches dug in the ground-in which they slept, ate and fought against the enemy.
  • The Treaty of Versailles, signed in 1919, was one of five peace treaties signed after the Central Powers surrendered to the Allies. Germany was forced to acknowledge guilt for the war, pay the other countries for the damage they caused, and reduce the size of its armed forces. It was also forced to return territory it claimed during the war to France, Poland, Belgium, and Denmark. After unsuccessful protests, Germany reluctantly signed the treaty.

See World War I for more details about the dates and events of this war.

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