The telegram came from from U.S. Ambassador to Britain Walter Page. At the time, Britain and Germany were at war. On its second page (show; click to enlarge) is the translation of a decoding of a message from German Foreign Minister Arthur Zimmermann sent to the President of Mexico in which was proposed an alliance between Germany and Mexico and were disclosed German plans to begin unrestricted submarine warfare.
In addition the telegram informs President Wilson how the British had intercepted and deciphered what history now refers to as simply "the Zimmermann telegram." The telegram was a significant development in the United States' decision to go to war alongside such nations as Britain and France against Germany and her allies including the Austro-Hungarian Empire.