The Zimmermann Telegram – Germany’s Secret 1917 Proposal to Mexico

In January 1917, German Foreign Secretary Arthur Zimmermann sent a coded diplomatic cable to the German ambassador in Mexico, Heinrich von Eckardt, instructing him to propose a military alliance.

Key Points

• If the U.S. entered WWI, Germany would support Mexico in reconquering Texas, New Mexico, and Arizona.
• Mexico would also mediate Japanese entry on the Central Powers’ side.

Interception & Impact

• British Room 40 cryptographers decrypted the telegram.
• Shared with U.S. President Wilson (Feb 1917).
• Published 1 March 1917 → public outrage.
• Contributed to U.S. declaration of war on Germany (6 April 1917).

Historical Significance

The telegram is a textbook case of signals intelligence altering geopolitical outcomes. Mexico, embroiled in its own revolution, declined the offer.