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.…
— Telegram of January 19, 1917
This telegram was part of an effort to
(1) form an alliance between Germany and the
United States
(2) convince several western states to secede
from the United States
(3) bring Mexico into World War I on the side of
Great Britain and France
(4) enlist Mexican support for Germany if the
United States declared war
This telegram was part of an effort to "(4) enlist Mexican support for Germany if the United States declared war" This type of submarine warfare is what brought the US into the war.