The following was sent by Germany to Mexico 100 years ago.
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.
Signed, ZIMMERMANN
Just a thought. I guess they did not want California back even then.