The NATO forces defeated the Taliban in a timeframe that could be measured in hours. The remaining years were an exercise in nation building, there was never “defeat.” The military simply isn’t the right tool to lift a nation out of poverty and eventually the voters got bored.

In Vietnam, the US was fighting an army backed by the Soviet Union and China that had anti-aircraft and artillery.

No, the US insurgency would turn into a Grozny unless the insurgents get backing from China or some other serious player.

Think of a rebellion as national "unbuilding" and you get some idea of how things might go.

If things get that hot, there will be substantial defectors and various state and federal security services fighting each other.

I don’t think it’d be easy to get a Chinese ABM to Minneapolis without anyone noticing.

What could happen in this scenario would be either local military defecting or guerrilla warfare while the US military targets them from afar. You can easily bomb anyone back to Stone Age in hours, but taking control of the ground can be a lot more challenging if the locals don’t cooperate.

Anyway, a full-on civil war is a very unlikely - and undesirable - scenario.