World War I
Germany also wrote a secret telegram note to Mexico in code that suggest that both countries work together to attack the United States. This note is called the Zimmerman Telegram because it was sent by Arthur Zimmerman. It offered Mexico land in the Southwestern United States that the United States had taken in the Mexican-American War. British spies found out about the note and told the United States. The Americans became angry, and many decided that their country should enter the war against Germany. The Zimmermann Telegram and the sinking of American ships by German U-boats made the United States on April 6, 1917 declare war against Germany and join the Allies.