You’re getting there, but I think you’re seriously underestimating the amount of time it would take to get power back. If a country wants to destroy the United States they don’t even have to bomb a single city. A single nuke even half as large as most modern nuclear weapons detonated above the United States would destroy the entire us power grid. A destroyed grid means you have to replace every single piece of electronic equipment that uses a transistor from scratch, and with no factory to make new ones. Getting power back to the entire US would take years. Bringing back around to modern politics, there is no reason (other than selfish desire) besides this to own assault weapons. If something like this we’re to happen, anyone that doesn’t have a gun would be in serious trouble.