On 23 February 1917 the British relayed to the United States a telegram from German foreign secretary Arthur Zimmermann to t h e German minister in Mexico. The telegram read:

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 Mex-: ico 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 Mexico] 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...