I'm sure the USA would be a huge pain in the ass for any armed invader in any case.  Too many guns, too many people waiting for a time to use them.  Not saying it wouldn't be a turkey shoot if, having defeated the US Air Force (a snowball's chance in hell of that happening anytime soon) they rained fire down on the civilians beneath.  Even a .338 Lapua won't shoot anywhere near as high as jets fly.  Still, yeah it would be hell for an occupying force. All that aside, if something like that, or a huge natural disaster happened like a meteor impact or Yellowstone erupting, the fatties are fucked.  Because I am a compassionate man, but I for one am not going to do shit for any lardass when the effort thus expended may cost one of my family members his or her life.  So OK, fatty needs me to help get his mobility scooter up over the curb so he can continue on down the road?  Yeah, I'll help to keep my conscience clear.  But then fatty needs me to help protect him because a roving band of scavengers is coming up the street faster than his mobility scooter will drive.  Sorry, dude, but that's not my problem.  They need to get right now if they want to be right when it matters most.