The correct option is:
A promise by Germany to Mexico to restore lands lost to the US.
The Zimmerman Telegram was a secret diplomatic communication sent by the German Empire to Mexico in January 1917, proposing a military alliance against the United States in the event that the US entered World War I. It also offered Mexico the territories of Texas, New Mexico, and Arizona if Mexico joined the war on Germany's side. This telegram played a significant role in bringing the US into the war.