I doubt anyone will invade the us. China, if it had any military movement, is much more likely to want to consolidate everything close to it. Japan, eastern russia, the philippines, korea. Canada doesn't have the motivation to invade (it might allow areas to join if our military is dead enough to not fuss about it), and mexico doesn't have the wherewithal to use their military against the cartels (they did let their military loose once and it was kicking some ass, but they stopped because of internal reasons), much less a foreign country. They might annex parts of the southern states, in the same manner as canada if the military is done for.

India definitely doesn't want to suddenly build the logistics to invade, no south american country wants the headache, and european areas will probably be looking to their east.

Russia might be the only one with the motivation and quasi-ability to do it. They wouldn't get much more than they are currently out of ukraine, but it's possible putin would make a play for alaskan territory. I think it's unlikely, considering china would really take advantage of that extended and vulnerable supply chain.