The Zimmermann Telegram

What happened

German Foreign Secretary Arthur Zimmermann sent a coded telegram proposing a military alliance with Mexico against the United States, offering to help Mexico regain territory in Texas, New Mexico, and Arizona. British codebreakers intercepted and decoded it and passed it to Washington; its publication in March 1917 inflamed American opinion.

Why it matters

Coming alongside Germany's renewed unrestricted submarine warfare, the telegram helped push the United States toward declaring war.

Sources

• U.S. National Archives. Zimmermann Telegram (1917) · Primary source