Final answer:
The United States entered World War I in 1917 and played a significant role in helping the Allied forces secure victory.
Step-by-step explanation:
In what year did the U.S. enter World War I?
The United States entered World War I in 1917. Until then, the U.S. had maintained a policy of neutrality, but factors such as the sinking of the RMS Lusitania by a German submarine and the Zimmermann Telegram, which proposed a military alliance between Germany and Mexico, led to the U.S. joining the war.
Once the U.S. entered the war, it played a significant role in helping the Allied forces secure victory. The American Expeditionary Forces fought alongside British, French, and other Allied troops.
Learn more about U.S. entry into World War I