Zimmermann note, secret telegram sent on Jan. 16, 1917, by German foreign secretary Arthur Zimmermann to Count Johann von Bernstorff, the German ambassador to the United States. In it Zimmermann said that in the event of war with the United States, Mexico should be asked to enter the war as a German ally. In return, Germany promised to restore to Mexico the lost territories of Texas, New Mexico, and Arizona. British intelligence intercepted and deciphered the telegram and sent it to President Woodrow Wilson, who released it on Mar. 1, 1917, to the press. The Zimmermann note helped turn U.S. public opinion against Germany during World War I and strengthened the advocates of U.S. entry into the war.
See B. W. Tuchman, The Zimmermann Telegram (1966).