As I recall, there was not much interest in Texas one way or another by anyone untill the good folkes from the east began moving here. Nuthin but wild cattle, native indians and cactus. As soon as the you-know-what people started moving in, developing land, establishing civilization and in general improving the situation with HARD WORK AND SWEAT, well, now, it was a whole new ball game.
As far as mexico taking Texas, F-A-T C-H-A-N-C-E. I-10 was posistioned for that very reason, to allow defense of the u.S./mexico border. Ft. Hood is where it is for a reason. Pantex nuke facility is where it is for a reason.
If some dope smokin La Raza airhead or a still halucinating Aztlan "follower" really believes Texas will roll over and give it up for the skum further south ain't been to a good 'ol Texas Gun Show in about 20 years. There is more firepower stacked in closets in Texas than in most third world armories around the globe. Higher quality and more sealed and crated ammo too. And they are just praying to be the first to spot such an idiot thinking this is real . . .
it'll NEVER happen. Like the man said, they tried it before, not a good idea.