Question

What was a major factor that led the United States to enter world warI?

Answer 1

Remember, World War 1 was the first of two wars, which started on July 28th, 1914 and ended on November 11th, 1918. 
A major factor that led the United States to enter World War 1 would be because of Germans attacking American ships that had Americans on it, using submarines. Another reason would be because of a British telegram, called the Zimmerman Telegram/Note, that offered an alliance between Germany and Mexico. 

~Hope I helped!~

Answer 2

Two major factors that caused the U.S to join WWI, was the Zimmerman Telegram, and Germany's announced intention to resume unrestricted submarine warfare. I hope I could help :)!