B. unrestricted submarine warfare and the zimmerman telegraph
The Zimmermann Note, or telegram, was sent by German Foreign Minister Arthur Zimmermann. He sent it to his ambassador in Mexico and the goal was to get Mexico to become an ally of Germany. It said that Germany would, after it won the war, give the Southwestern US back to Mexico. The United States entered the war because of the Germans' decision to resume the policy of unrestricted submarine warfare, and the so-called "Zimmerman telegram."
