US President Woodrow Wilson on April 6, 1917 declared
Germany's unrestricted U-Boat warfare was only too successful, by the end of February 1917, 781,000 tons of shipping had been sent to the bottom of the Atlantic Ocean.
Woodrow Wilson the US President was getting very upset at the number of US ships targeted by the German U-boats, and the loss of life of American merchant sailors.
What must have been the last straw was the sinking of three US merchant ships over only three days, these were:
March 16, 1917.
March 17, 1917.
March 18, 1917.
The President had had enough.
Several key events leading up to this act included the sinking of the Lusitania in 1915, and the Zimmerman Telegram sent to Mexico by Germany in January 1917. The resumption of unrestricted submarine warfare by Germany on February 1, 1917 was a key event that turned the American public from neutral ground at home to the trenches of Europe.