When did the U.S enter the world war 1?

Answer 1

1917

Answer 2

The US declared war on April 6, 1917.

However, it took time to mobilize soldiers for the army, and US forces were not fully engaged in France until the Spring offensive of 1918. This allowed the US forces to be engaged to the greatest effect along many of the lines of battle. After Germany lost most of its territorial gains from the early part of the war, they were forced to end the war on November 11, 1918.

Although Woodrow Wilson opposed US involvement, he came to see it as unavoidable, given Germany's submarine warfare against US shipping. An attempt to draw Mexico into the conflict (the Zimmerman Telegram) also helped to sway US opinions.

(see related questions)

Start of WW I

April 6, 1917
The US entered World War One on April 6, 1917. This was a declaration of war by the US Senate.
US declaired war against Germany on April 6, 1917 and later the same year against Austria - Hungary, December 7, 1917. The war came to an end on November 11, 1918 [armistice]. The Versailles treaty was signed on June 28, 1919.

Answer 3

In spite of the fact that many Americans wanted the country to remain neutral, the United States entered World War I on April 6, 1917. World War I ended on November 11, 1918.