Texas seceded&#x2F;rebelled, and became its own republic, as did Rio Grande, Yucatan, parts of Zacatecas, Jalisco, and Tabasco (and then Alta California after the USA got involved).  So yeah, &quot;Mexico&quot; didn&#x27;t start the war.  Santa-Anna, the specific person, started all those ensuing wars when he suspended the constitution and centralized power, pissing off just about everyone more than an arm&#x27;s length from Mexico City.  The only rebel republic that survived the retaking effort is the one that allied itself with the USA.<p>Had Mexico <i>not</i> gone to war with Texas and the USA, it is very likely it still would have lost all that territory to rebellion.<p>The secession tension grew into Mexico&#x27;s first civil war (Reform War of 1857-1861), which ended just as the USA-CSA civil war (1861-1865) was starting.<p>And if we&#x27;re talking &quot;at gun point&quot;, Guadalupe-Hidalgo was negotiated with USA occupying Mexico City.  There was serious consideration given to annexing <i>all</i> of Mexico.  Really, one major reason Mexico still exists at all is good ol&#x27; USA racism: all those Indians and mixed-race people would get to vote and elect their own representatives.  Also, would the Mexican states be slave states or free states?  So the USA pretty much just took only as much land as it could fill up with free white people, and paid off the loser.<p>And so they each got to have their own separate civil wars, instead of one big one.