Answer:
The Zimmerman Note was a telegram that Germany was sending to Mexico, but it was intercepted and deciphered by the British. The Germans wanted to create an alliance with Mexico. If Mexico helped Germany in World War II, then Germany would help Mexico gain back territory they lost to the United States.
This note angered Americans. Most Americans wanted to stay neutral and not get involved with the war, but this event changed their opinions. After this note, most people wanted to join the war.