Within this secret message, Zimmermann revealed Germany's plan to restart unrestricted submarine warfare as well as offered Mexico territory from the United States if Mexico were to declare war on the United States.
When the British shared the contents of the Zimmermann Telegram with the United States, the American public was outraged. Instead of World War I being contained to Europe, which seemed far away, the American public now felt the war was being brought to their own land.
The Zimmermann Telegram helped change public opinion in the United States away from isolationism and toward joining World War I with the Allies.
The Full Text of the Zimmermann Telegram
(Since the coded Zimmermann Telegram was originally written in German, the text below is a translation of the German message.)
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.