The Zimmermann Telegram
In January 1917, the British intercepted a coded telegram from German foreign secretary Arthur Zimmermann to Germany's ambassador to Mexico that offered to assist Mexico in reconquering U.S. territory in exchange for joining the Central Powers against the Allies should the United States declare war. In early March, U.S. papers published the contents of the telegram, and on March 5, 1917, the text was entered in the Congressional Record. Playing on fears of what would happen if Americans did not unite behind the war effort, cartoonist Clifford Berryman drew a hand in a gauntlet (decorated with the imperial German eagle) carving up a map of the southwestern United States.
On the 1st of February we intend to begin submarine warfare unrestricted. In spite of this, it is our intention to endeavor to keep neutral the United States of America.
If this attempt is not successful, we propose an alliance on the following basis with Mexico: That we shall make war together and together make peace. We shall give general financial support, and it is understood that Mexico is to reconquer the lost territory in New Mexico, Texas and Arizona. The details are left to you for settlement.