If and when the U.S. does collapse economically, and develops into chaos, does one think that Mexico, China, and Russia, will not take advantage of that? America had the rare advantage of being inhabited by a less than technological populace, i.e. the American Indian, and the white European was able to "progress at a steady pace" by repressing them, with the aid of their however crude, but advanced technology.
We are now, on a par with the rest of the world, having sold our technology to others, and will most likely become, just another third world country, thrown into chaos, by a spoiled, I want it now culture of youngsters, whom have had everything handed to them. It would take decades to recover, and perhaps we never would.
Imagine trying to teach a kid that has never done anything other than play videos, or rode a skate board into his thirties, how to even build a fire to stay warm.