How one telegram helped pull the US into war

A message meant for Mexico

In January 1917, Germany’s foreign secretary, Arthur Zimmermann, sent a coded telegram to the German minister in Mexico. It proposed an alliance if the United States entered the war against Germany: Mexico would fight alongside Germany, and Germany would support Mexico in recovering territory it had lost to the United States, including Texas, New Mexico, and Arizona.

The proposal was meant to create a problem on America’s southern border. If the United States had to confront Mexico, Germany hoped, it would have fewer troops and resources to send against Germany in Europe. But the offer was also a gamble: Mexico had little reason to believe Germany could deliver the promised territory, and the country was already occupied with its own revolution.

How the secret became public

British intelligence had obtained the telegram and deciphered it. Britain faced a delicate choice: reveal the message and risk exposing how it was reading German communications, or keep quiet and let the proposal remain secret. British officials arranged for the telegram to reach the United States through a route that would not immediately reveal the full source of their intelligence.

Once American newspapers published it in March, Zimmermann himself confirmed that the message was genuine. That confirmation made it harder for Americans to dismiss the story as British wartime propaganda. Mexico ultimately did not accept Germany’s proposal.

A turning point, not the only cause

The telegram gave Americans a vivid reason to fear that Germany’s war might reach the Western Hemisphere. It strengthened support for entering the conflict, especially amid existing anger over Germany’s submarine attacks on ships carrying Americans and American goods. The United States declared war on Germany in April 1917; the telegram helped shift opinion, but it was not the sole cause.

Germany’s attempt to distract the United States instead made the threat feel immediate. A plan designed to draw Mexico into the war gave American readers evidence that Germany was willing to enlist a neighboring country against them.