War. People say it can't, but that's just hope/optimism speaking
Personally I'm thinking this all goes sometime in the 2020s, with 2020 being the earliest. By then the russians, chinese, elite should have all of their war/post-war preps complete. Then the economy globally will be allowed to fall and the usa will most likely be sneaked attacked.
Probably will be a two prong attacked.
1.An American blackout type attack on the infrastructure. Except shyt doesn't magically come back after a week. Nor are other nations sending supplies.
2.While 1 is happening, but before the usa realizes what's happening.. 2 will take place. A Nuclear assault on military installations, known usa-elite bugout locations, some major cities.
Not sure if major cities will get hit tho. a week of no food, water, energy, will turn a place like NYC into an all out orgy of violence, murder, and rape. Nuking NYC, LA, etc would be doing those places a favor