The Zimmermann Telegram: Why The US Joined The Allied Powers

Photo Credit: Universal History Archive/Universal Images Group via Getty Images

It is believed today that few decoded messages have had the global and historical impact that the Zimmermann Telegram had in 1917. This single telegram gave the U.S. the boost it needed to join the First World War in Europe, leading to the end of the war and the aftermath that would lead the world into the even more destructive Second World War.

Before the Zimmermann Telegram, the U.S. was happy to stay out of the war

The telegram was the culmination of a years-long effort by Germany to start a war between Mexico and the U.S. Germany hoped that with America fighting a war with Mexico, they would have limited capacity to join the war or provide resources to the Allied armies in Europe. At one point, Germany even sent a Mexican military official a sum of well over $10 million dollars to begin a war with the U.S.

Keeping the U.S. and its crucial exports away from Europe was massively important to the Central Powers, as at the time Germany believed they could achieve victory in Europe as long as America was not on the scene.

German U-boat circa 1915.
German U-boat circa 1915. (Photo Credit: Photo by Jacques Boyer/Roger Viollet via Getty Images)

Earlier in the war, Germany was stopping U.S. exports by attacking merchant shipping in the Atlantic with their terrifying submarine fleet. In 1915, Germany began employing tactics close to unrestricted submarine warfare, attacking any ships that came into a specified area. This limited the imports arriving in the U.K. by sinking them before they could make land, and it affected the number of ships sent, due to fears of their destruction.

This became so brutally effective that the U.S. (who at this point was not actively involved in WWI) demanded that Germany stop. Thankfully, they did, for a while at least. By 1917, Germany planned to begin unrestricted submarine warfare once again in a last-ditch effort to starve the British. This would begin on February 1, 1917.

They knew that an all-out assault on U.S. merchant shipping would bring America into the war, but estimated that if they could delay the U.S.’s involvement, they could beat the starved British and French in Europe before they arrived.

This is what the Zimmermann Telegram was for.

The telegram was Germany’s doomed plan to keep America occupied

The Zimmermann Telegram was sent on January 17, 1917, by Arthur Zimmermann from the German Foreign Office, to Heinrich von Eckardt, Germany’s ambassador to Mexico. The telegram would inform him that if, after Germany resumed their submarine attacks on Atlantic shipping, America looked poised to enter the war, he would present Mexico with an offer to declare war on the U.S., with German funding.

Zimmermann portrait
Arthur Zimmermann, State Secretary for Foreign Affairs. (Photo Credit: Universal History Archive/Universal Images Group via Getty Images)

The actual telegram reads:

“We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona.

“The settlement in detail is left to you. You will inform the President of the above most secretly as soon as the outbreak of war with the United States of America is certain, and add the suggestion that he should, on his own initiative, invite Japan to immediate adherence and at the same time mediate between Japan and ourselves. Please call the President’s attention to the fact that the ruthless employment of our submarines now offers the prospect of compelling England in a few months to make peace.


Translation of decoded Zimmermann Telegram
Translation of the decoded Zimmermann Telegram.

The Zimmermann Telegram, as it became known, was sent through U.S. communication cables that ran through England, and unknown to the Germans and even the U.S. at the time, every message that passed through was monitored by the British.

The telegram was intercepted by the British and sent to their codebreakers. They managed to decipher the coded message in a short amount of time, thanks to secretly cracking German codes long beforehand.

Once decoded, the British were alarmed at the message. As they had been trying for a long time to bring America into the war, and they knew they had the perfect opportunity to make this happen. However, by announcing the telegram to the American public, Germany would discover their codes had been broken and the U.S. would realize the British were listening to their communications.

To solve this, the British devised a plan where an agent would obtain a copy of the message in Mexico, which would then be shown to the Americans. The message that arrived here was encoded in an older code, one that the British deemed worthy of the Germans finding out they had cracked in exchange for the U.S. joining the war. With both the main problems solved, the British presented the message to the U.S.

The message, combined with Germany restarting unrestricted submarine warfare, enraged the American people, who switched gears from opposing involvement in WWI to actively seeking it. Just three months after the Zimmermann Telegram was first sent from Germany, the U.S. officially joined the war. A little over 18 months later, the war ended with Germany’s defeat.

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While the U.S. response is the most impactful, the Mexican response is perhaps the most ironic. After receiving the message, Mexican President Venustiano Carranza sought the opinions of his military officials on Germany’s offer. They concluded that a German-backed war with the U.S. was not in Mexico’s best interests, thanks to political instability, a vastly inferior army, and wanting to avoid upsetting relations with South American nations.

So, the Zimmermann Telegram was intended as a way to make sure America stayed out of the war and to guarantee a German victory in Europe. Instead, it caused the immediate and nationally supported declaration of war by the U.S., mobilizing troops and reinforcing the Allies in Europe, leading to Germany’s eventual downfall.