Answer:Sinking of American merchant ships
Explanation:In early 1917 Berlin forced the issue. Its declared decision on 31 January 1917 to target neutral shipping in a designated war-zone became the immediate cause of the entry of the United States into the war.
I believe it was the Stock Market Crash of 1929
Prevent the incalculable loss of life it would take to invade mainland japan.
Explanation:
Britain attacking the Western United States