Zimmermann Telegram

The Zimmermann Telegram was a secret coded diplomatic cable sent on 16 January 1917 by the German state secretary for foreign affairs, Arthur Zimmermann, to Heinrich von Eckardt, the German minister in Mexico, during the First World War. It instructed von Eckardt to propose a military alliance to the Mexican government in the event that the United States, then still neutral, entered the war against Germany: Germany would provide Mexico financial support and help it reconquer the territories of Texas, New Mexico and Arizona, lost to the United States in the nineteenth century. British naval intelligence intercepted and decrypted the telegram and passed it to the United States government, which published it on 1 March 1917; Zimmermann himself publicly confirmed its authenticity two days later, removing any doubt that it might be a fabrication. The revelation caused public outrage in the United States, at a moment when German unrestricted submarine warfare had already strained relations, and it became one of the key factors pushing American public and congressional opinion toward the declaration of war on Germany that followed in April 1917. Historians have called the interception and decryption one of British intelligence's greatest successes of the war and among the earliest instances of signals intelligence directly shaping the course of world events.