How did germany's use of unrestricted submarine warfare bring america into world war 1

This site may help you:
https://quizlet.com/58430275/71-the-us-enters-wwi-flash-cards/

to save you from googling i believe the answer to your question is:
In 1917 the use of unrestricted German submarine warfare caused the U.S. toenter the war on the side of the Allies. How did Germany's use of unrestricted submarines warfare bring the United States into WWI ? A German U-boat had sunk the British passenger ship the Lusitania at great loss of life.

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