Question

(MC)Which factor contributed to the entry of the United States into World War I? the imminent collapse of the Allies’ defenses German submarine attacks on American ships overwhelming public support for the war effort Mexico’s declaration of war on the United States

Answer 1

One of the major factors that contributed to the entry of the United States into World War I was "German submarine attacks on American ships," since the Germans were practicing "unrestricted" sub warfare. 

Answer 2

The factor that contributed to the entry of the United States into World War I was German submarine attacks on American ships (OPTION 2).

On January 31, 1917, Germany suspended unrestricted submarine warfare in the North Atlantic and the Mediterranean putting American ships at risk again. Before formal German's declaration, it had already broken its promises to restrict submarine warfare during the WW I and had caused the sinking of several U.S. ships before, and Americans had forgiven them every time.

However, this Germany's announcement was enough for the U.S. to finally end diplomatic relations with Germany on February 3rd and the decision was reassured when, the same day, Germany provoked the sinking of the private American cargo ship Housatonic. It was torpedoed by a submarine. Fortunately, no one was on board.

This led to the United States to enter into World War I on the side of the Allies, in April of that same year.