In case of a US annexation of Mexico's northern states (from coast to coast), the US borders shifts south and becomes a lot shorter and easier to defend.History Learner wrote: ↑29 Jan 2021 03:45Significantly less; all of the above had foreign patrons they could funnel money, arms, and training into them while Mexico couldn't. North Vietnam, due to both its land border with China and restrictive ROE on the part of the U.S. with regards to Haiphong harbor, had most of its war effort bank rolled by the Chinese and Soviets. Mexico, on the other hand, has a border to the north with the United States, to the South with U.S. clients and its two ocean borders are secured via the U.S. Navy. Add in American control of the cities, and any insurgency is going to quickly starve out of logistics.
For instance if the line Puerto Vallarta to Tampico becomes the new southern border of the US. That leaves the major cities and majority of the population outside, which saves a lot of trouble. Still there would be a huge territory to police and pacify - continuously. Though rebel action would soon be quickly subdued, isolated pockets of resistance may linger on while other groups might go underground or temporarily disband. It would be impossible to cut of all ties to the south: free Mexico. And this time it wont be like the 19th century: there is telephone, telegraph and radio. the voice of a Radio Mexico Libre will keep feeding hope to the oppressed Mexicans in the north. There will be tensions there with new arrivals from the old US, Yankees to run businesses, mines and local govt. Indian territories might have to be pacified again or relocated when US companies start exploring the land. I would still say: a hell of a job and not really worthwhile.
Even an occupation zone ending at a line farther north, for instance the southern borders of the states of Sonora, Chichuahua, Nuevo Leon, Tamaulipas, etc, would be a challenge to police, though with much less new citizens to control, a bit more feasible.