I'm interested in this! I have a couple of ideas for factions:

Confederate States of America

I thought maybe that a successor state to the Civil War combatant may be interesting. A group that uses their flags and such, and also uses slavery as a basic practice. Not just black people though, cause there wouldn't be enough slaves otherwise to get anything done. 

I'm no American but North Carolina was one of the founding states of the CSA, wasn't it?

Enclave

Not really a new faction, but a cool one. And I have a hard time believing that they spent from 2077 to 2242 on that little oil rig. So yeah, they're fun.


Chinese People's Republic

A community/state formed by descendants of a Chinese army that had landed in the US after the bombs fell. They could be led by a council of Ghouls, veterans of the original army from before the war.essentially a communist state.

Any of these sound good?