This is all so fucking stupid.
The idea that we would be evenly split and given to the closest countries to each respective region is just hilariously simplistic. After the concept of Fed govt fails the states would gain full control, and private capitalization of industry through state govts would keep the economy and the military functional. We would still be very much able to defend ourselves, especially after pulling all of our troops back onto our own soil.
Secondly, if the US collapsed there would be nothing to support all of the illegals and therefore no incentive for them to cross the border anymore. Also, they wouldn't just be facing deportation, they would be facing a bunch of pissed off Americans defending their land for all it is worth. The only real incentive they would have to come into AZ and TX etc would be to defend their relatives as we kick em out.