It seems to me that depending on your endings, sides retreat or stop the annexation to help their own faction. It looks almost like were beginning to form new commonwealths,
NCR Land, DC Brotherhood, Legion Land, each close to being the size of a commonwealth.

Possibly new America forming?

I would say so.
The way the game ends if the obvious one is canon, three states are left.
The NCR don't fall properly...
Just sent back to their borders with some of what they came for ( Power, technology and resources ) still provided, at a price.

CL get a kicking, lose face and are reined in for a while, making intercine conflict or at least a long look at rebuilding likely.

House gets what he wants.
The rest of the Mojave independent and likely to establish links with each other.

3 States reborn.

NCR control all of California and then some. They have States and Territories. Legion Control All of Arizona and then some. Not sure how they control it. DC BoS control tinny little DC.

I would say no.

yea bos contols parts of dc since supermutants roam everywhere.
ncr controls california and havent heard if they control any other state.
legion controls all of arizona,parts of colorado,parts of utah,and i believe parts of new mexico

BOS in DC I'm assuming is flourishing since most likely they have been purged from 87, the GECK flowing, and nearby people to join. With them hunting mutants and the mutants base (most likely) destroyed, they are a dyeing breed in DC

I don't see BoS as being that much interested in making a commonwealth for themselves. With Lyons not charging for the pure water, they actually lose resources keeping the purifier up.

Ashur probably have a better chance of carving out an empire out of Pittsburg if he stays in power and a cure is found.

I thought the states in FO were bigger less 50 states and more 13 of them ( or commonwealths as called ).
If so the NCR and CL would cover two of the old ones, Mojave a third, east coast a fourth, mid west a fifth.

That info comes from a board game J.E Sawyer never made based on Fallout. I don't see it as canon but it does sound cool.

OH I did not know that Styles thanks, I took it as fact and have seen it used as such before.
It does rather look and sound cool, I'll post the link for others to check out.
http://fallout.wikia.com/wiki/United_States_of_America

The odd thing though some times you here about states, then commonwealth and vice versa in FO.
I know the US has some Commonwealths IRL, however I'm not sure those are actually in game.

Many states still call themselves Commonwealths one of them being Massachusetts.