The Zimmerman Note was supposed to be a secret telegraph from the German government to the Mexican government. The goal was to get Mexico to attack the United States so that the US would not interfere in World War I. The Germans promised that if Mexico did this, they would get back the land they lost to the US in the Treaty of Guadalupe Hidalgo.
Ultimately, this note is intercepted and the US finds out about this before it reaches Mexico. Shortly after this, the US enters World War I.
