US wanted to be neutral, but these events made US get involved:
Sinking of the Lusitania, 1915 – germans sank a ship containing US passengers
Unrestricted Submarine Warfare – germans sunk all ship entered the war zone, some american ships
Zimmerman Telegram – note sent to mexico where mexico would start a war with the US; when the conflict was done in europe germany would help mexico gain land last in mexican american war. Discovered germany’s hostile intention towards the US