The Zimmermann telegram

In January 1917, British code-breakers in the secret Room 40 office intercepted a telegram from German Foreign Secretary Arthur Zimmermann to his ambassador in Mexico. It proposed a wartime alliance: if the United States entered the war against Germany, Mexico should join Germany and Japan against America, with Germany's help in reclaiming Texas, New Mexico, and Arizona.

Barbara Tuchman traces how Britain's codebreakers deciphered the message, and the delicate problem of how to hand it to Washington without revealing that Germany's codes had been broken. She sets the telegram against the wider background of the German high command's decision to resume unrestricted submarine warfare, Woodrow Wilson's strained neutrality, and the unstable state of U.S.-Mexico relations during the Mexican Revolution.

When the telegram's contents reached the American press in early 1917, public opinion shifted decisively, and Congress moved toward a declaration of war against Germany within weeks. Tuchman's account follows the intelligence operation from interception to publication and its role in bringing the United States into the First World War.