The Zimmermann Telegram and America’s Entry into World War I

By Nolan Nelson

On April 6 one hundred years ago, the U.S. declared war on Imperial Germany.  The Zimmermann Telegram finally prompted the decision Great Britain had been wishing for.  The text asked the Mexican government to enter the war on the side of Germany, if the U.S. declared war when Germany resumed unrestricted submarine warfare in February 1917.  The German ambassador offered for them to make war and peace together, offered generous financial support, and to sustain an understanding Mexico was to re-conquer the lost territory in Texas, New Mexico, and Arizona.

The British were monitoring messages neutrals such as the U.S. and Sweden were improperly forwarding for the Germans, because they were enforcing a tight blockade of Trans-Atlantic cable use.  One time they complained of such practices, but in such a way that they convinced the Swedes and Germans that though the messages contained German code groups they could not read them.  The Swedes stopped using this particular path, but found other ways to work around the prohibition.  The British then decided there was more to be gained by allowing the evasions, because they could actually read entire German messages.

For this fatal message, the German Foreign Minister Arthur Zimmermann used two of these new paths to contact his ambassador in the U.S., who then contacted the Mexicans through the German ambassador there.  Now the British had the very thing that could bring the U.S. into the war, but through methods and channels considered too useful to be revealed.  Especially since they involved decrypting messages sent through Sweden and the U.S.

The British solved their dilemma by devising the subterfuge of using the telegram as received in Mexico.  They didn’t have a copy, but their agent “T” obtained a copy from the Mexico City telegraph office.  Two suspicions were confirmed that it was transmitted in an old code and that several details were changed in retransmission.  They could now bring the message to the Americans without revealing that they were reading newer German codes or that they knew about these channels for the evasion of neutrality.  The British presented the telegram with the following cover message.

“Early in the war the British government obtained possession of a copy of the German cipher code used in the above message and have made it their business to obtain copies of Bernstorff’s cipher telegrams to Mexico, among others, which are sent back to London and deciphered here.  This accounts for there being able to decipher this telegram from the German Government to their Representative in Mexico, and also for the delay from January 19 until now in their receiving the information.  This system has hitherto been a jealously guarded secret and is only divulged to you now by the British government in view of the extraordinary circumstances and their friendly feeling toward the United States.  They earnestly request that you keep the source of your information and the British government’s method of obtaining it profoundly secret, but they put no prohibition on the publication of Zimmermann’s telegram itself.”

Now the British and Americans faced the task of conspiring to prove the validity of the telegram without revealing the supposed source.  The German Foreign Minister removed this conundrum himself by unexpectedly confirming the telegram was genuine.

Wilson could present the case that unrestricted submarine warfare plus the telegram constituted a virtual Pearl Harbor and enough folks bought the logic. Zimmermann could have probably bought a few months of time by using the old tactic of denying everything and making counter charges. But, he didn’t. 

On April 2, 1917, President Woodrow Wilson asked Congress for a declaration of war against Germany. On April 6, Congress granted the request and the United States was formally at war with Germany.

The Americans arrived just in time in Europe.  The Germans had broken through the last French defenses and were on their way to Paris when they ran into the U.S. Army and the 4th Marine Brigade at Belleau Wood in June of 1918.

The Battle of Belleau Wood would become another heroic chapter in the glorious history of the US Marine Corps. Five months later, on the eleventh day, of the eleventh month, at the eleventh hour, World War I ended. The Zimmermann Telegram had paved the way for US involvement in the war, which turned the tide toward eventual Allied victory.