how is civilization rebuilding, new vegas is empty as hell
I have to agree with this. Why do almost everybody live in tents and run downed buildings? because there not rebuilding. If they were that wall along the strip should have been rebuilt because it looks like sh*t. Not to mention that in most towns they dont even help to rebuild some of the buildings or make them more attractive.
To rebuild a society, you need a working beginnings of one. Look how NCR fares, the Legion, the Strip with Mr. House. There you have some early societies that all are striving towards some form of rebuilding. And you gotta remember the situation the region is in, and that building a nation doesn't happen in one night, and without a (forced or voluntary) unity of the people in it.
And most of the population in the Mojave is concentrated at the center, which is in the best condition. There is no need for the majority of the people to be scattered around the wasteland. Few selfsustained settlements still remain, but they are too to be annexed with who ever takes over tha land.