So would there be petty groups struggling to survive own their own or fighting to fill the new opening in the powerstcructure? Or player crafting his own faction?
I imagine it would be something similar to if Caesar's Legion fell, but these smaller factions didn't loose their identity when apart of this collapsed nation, or are completely new, and something born out of the collapse.
Basically I imagine this collapsed nation having had a governing system where there were different parties (political or simply influential enough groups) and factions, vied for control at one point or another through elections or something, and through various events throughout their collected history (both external and domestic), this nation gradually collapsed under it's own weight, leaving these old and new factions, to sort of pick up the pieces. Although, there would still be a faction of this collapsed nation, made up of the true believers (sort of like the Soviet government after the fall of the USSR, where there was still a group of Soviet holdouts,) all of who are looking to hold onto what little they have left to hold onto, not wanting to be erased from history.
It wouldn't be a story of one faction taking complete control in the end, like Caesar's Legion, NCR, or House in New Vegas, but simply a story of collapse and the extreme aftermath that can follow such an event. I haven't quite figured out where the PC story would fit into this all? Maybe just a person simply trying to help where he/she can, obviously seeing the good and bad of every faction (no absolute good or bad factions, simply different shades of grey,) and taking sides where he/she wants?
I think at the end of the game, it could end up being something like New Vegas' beginning, in the sense that these factions who were simply caught in this collapse, unsure of what to do next, and are once again in a situation to fight for absolute control of the land, and build a new nation of their own, if that makes sense.