The two events that pushed the U.S. towards entering WWI was the Zimmerman Telegram and the sinking of the Lusitania. The Zimmerman Telegram was a telegram from Germany telling Mexico to attack the U.S. in exchange of getting back the taken territory the U.S. "stole" during the Mexican-American War. The Lusitania is a ship that sank in 1915 caused by a German submarine firing its torpedo. It was a passenger ship that carries over 1,900 passengers, military and civilian (mostly civilians). Over 120 Americans died on the ship. There are also many other reasons why the U.S. enters WWI, but these are the major ones I know of.
