In the Telegram, Germany asked Mexico to join forces if the United States entered the war.

In addition to unlimited submarine warfare, the so-called "Zimmermann Telegram" was another reason for America's entry into the WWI. The telegram that Germany sent instructions to its ambassador to Mexico was intercepted and decrypted by the British Intelligence Service. In January 1917, with this telegram, Mexico was offered to stand on the side of Germany if it came to a future conflict between Germany and America with significant financial compensation.

The Zimmermann Telegram (or Zimmermann Note or Zimmerman Cable) was a secret diplomatic communication issued from the German Foreign Office in January 1917 that proposed a military alliance between Germany and Mexico in the event that the United States entered World War I against Germany.