I share your concern! It is already happening in many areas. Maybe we need to subsidise Mexico, what I mean is; build some new factories there that pay decent wages, do a new Nafta that works for us and them, and even take over most of the LE function from them. Build homes, whatever. Their gov.t is so dysfunctional as it is now. I can imagine a huge swarm of MILLIONS coming across the border during a famine, or economic collapse, and we would be almost helpless to do anything but major battle with them, and a lot of dead people.
Pancho Villa was right in his revolution, but the wrong people took over but the revolution was never fulfilled for its promise to the people.