Sent in 1917, the Zimmermann Telegram was a confidential message from Germany to Mexico promising Mexico territory in the United States if Mexico aided Germany should the United States enter World War I. The telegram convinced the American public to support the American troop deployment into the war effort.
In January 1917, German Foreign Minister Arthur Zimmermann sent the message to the German Minister to Mexico, Heirich von Eckhardt. The British, who were actively trying to decipher Germany's coded messages, partially deciphered it, revealing Germany's intentions. The telegram also made it clear that Germany decided to resume unrestricted submarine warfare, with the full knowledge that this decision would most likely force the United States to enter the war.