Avellone Fallout show the humanity recovering and the fall of the Brotherhood of Steel.
In F1 some of the communities are quite primitive scavengers but even there some have started to make something new already ...and the BoS have a massive edge of having the best technology, weapons and armour out of all the survivors.
F2 shows how those communities united and formed a democratic nation of NCR as well as the other villages. You still get places like the Den, the tribes and Klamath that are on the edge of civilization both by location and advancement. ...And the BoS have been outgunned by the Enclave and had to admit defeat for the first time in their history.
New Vegas shows how NCR has not only grown bigger but also gained better and better technology and is rich enough to be able to take over other regions (peacefully or by force. They at least contend to fight only raiders and creatures that are hostile without provocation (or so they say but basically it's Manifest destiny all over again. ...And the BoS have been destroyed nearly completely.
...Note that the BoS falls because they close themselves from the outsiders and stagnate while other communities grow and recover. They could have integrated themselves to the NCR and not have minded that they aren't the sole owners of technology, but they didn't and their arrogance drives them to war and defeat. But that's just something I always feel like I need to rant about.
More to the topic, even in F1 there aren't that many scavengers. Things that can be easily looted have been looted. Scavengers steal from other survivors. Bethesda Fallouts on the other hand have every single building filled with food and stuff from pre-war era as if no one bothered to get out from their hole to see if they could find more supplies. That and all the functioning lights and computers annoyed me enormously in F3. Why would people still scavenge after 100 years? The only places that still had loot in were places that were locked up and filled with radiation or robots that kept people out.
But my other, OTHER point is that the America had recovered. There were brand new nations here and there. Some violent and brutal like the Legion, some Democratic but flawed like NCR. Ulysses could have succeeded as he wasn't nuking everything, just a few locations that would have crippled the forces around Vegas and thus forced that area to fall again and see if something better grew from the ruins.
