January 16-17, 1917: The Zimmermann Telegram
Germany’s decision to resume unrestricted U-boat warfare at the beginning of 1917 was arguably the worst strategic decision of the First World War – but Germany dug the hole even deeper by attempting to start a war between Mexico and the United States. Together these ill-advised moves turned American public opinion decisively against the Central Powers, setting the stage for U.S. entry into the war in April 1917.
The secret initiative to bring Mexico into the war – which didn’t stay secret for long – was laid out in the “Zimmermann Telegram,” a coded message first sent by the German State Secretary for Foreign Affairs Arthur Zimmermann to the German ambassador to the U.S. Johann von Bernstorff, who passed it along to the ambassador to Mexico Heinrich von Eckhardt (this indirect route was used in an attempt to avoid interception, futile as it turned out; below, the coded telegram from Bernstorff).
In his previous role as undersecretary of foreign affairs Zimmermann enjoyed some success fomenting dissension abroad to distract Germany’s enemies from the…