One thing I don't understand is how there could be a resource crisis prompting a resource war if nuclear energy is the national norm. The war was over oil - not uranium or plutonium after all.
The resource wars began in 2052.
The first nuclear power cell wasn't unveiled until 2066, and was made by Americans, for Americans. Even then, it took MANY years to to get it everywhere in America, it basically wasn't until right before the war began that the switch over was complete.
Other countries lacked such a power source for some time, and even when they DID it get, relations between the various nations had spiraled so out of control it didn't matter, and war was impossible.
The resource wars began over oil, but they ended over petty hatreds, despite the problems being solved.
That's one of my peeves with the Fallout canon as a whole, actually. The West Coast has spawned the BoS, various major cities like the Hub and New Reno, the NCR, the Legion, the Master's army, and a motley crew of minor factions but still relatively advanced factions such as the Shi, the Followers and Broken Hills. But apparently the entire territory occupied by the Legion prior to its arrival was solely settled by 86 easily conquerable, random tribes? There are no significant settlements we ever hear about beyond the Core Regions save for New Canaan? No major power has sprang up between the West Coast and East Coast in 200 years? I get that we didn't spend much time outside the West or East coast, but it seems that the rest of the US is pretty empty.
The Commonwealth being underdevelopped is actually a plot point in FO4, because of the Institute's interference and the decline of the Minutemen. But otherwise it feels as if only NCR and the Legion have managed to become major powers over two centuries across all of the US. And I guess the Midwest/Maxson BoS, but the former is only sorta canon and the later is conditional on the player's actions.
The rise of the core region over others is actually fairly explainable.
-The core region had the most number of successful vaults anywhere. Vault 13, 15, 8, and the LA demo vault, all kept fairly large numbers of people alive through the war. Whereas the other 90% of vaults across America got their inhabitants killed.
-The core region also had a number of GECKs. Both Vault City and the NCR were built using GECKs to jump start them.
-And the core region, most importantly, had two super magical, almost god-like, player characters to fix and all of their problems for them, and set up the situation for it to survive. The other regions of America are primitive because they never had a Vault Dweller to save their Tandi, or a Chosen one to stop their Enclave.
There is also something to consider(note I didn't make the following up and am just repeating something I heard someone else say on a thread on 4-chan that I happen to agree with)
Large portions of America, specifically the northern states like Montana, Idaho, Wyoming, the Dakotas, etc. etc. historically have low populations due to isolation and harsh environments, even in the real world. Many of the towns up there aren't self sustaining, and would have quickly collapsed after an atomic war when local resources ran out. Everyone who didn't die in the war, or from the resulting radiation blanket, would have likely only had two options
A. Become hunter-gatherer peoples living off the land, like the tribals we see everywhere.
B. Flee their small towns with nothing in them and congregate around the nearest major metropolitan areas. We hear about this happening in places like Mexico City from Raul.
This would have left large parts of America that are already historically empty even MORE empty, and thus far less able to recover/rebuild, as there simply isn't the people for it.
When it comes to places like the four corners states, there is a similar, but also different, problem at play. Utah for example has 80%+ of its population in a small strip around and including Salt Lake City called the Wasatch front. Similarly, Arizona has something like 85%+ of its population contained in the cities of Phoenix and Tuson. Denver has like 60%+ of its population contained in the Denver metropolitan area. The rest of these states are just large stretches of nothing, with few valuable resources.
We hear in Honest Hearts that Salt Lake City was completely obliterated by nukes, it was nuked so hard it made the great Salt Lake evaporated completely, and Denver was abandoned entirely for some reason(IIRC Van Buren said it was because of radiation). We know places like Vegas got 77 nukes sent at them, so imagine how bad places like Phoenix and Tuson got hit. The vast majority of these states populations, even more so then the rest of the U.S., would have been wiped out in the war, since they all resides in just a few cities.
Any places that did survive with some level of civilization would have been largely self sufficient, and their closest civilized neighbor would have been so far away they likely wouldn't have even known that town exists, due to the hundreds of miles of desert between them, thus prohibiting any sort of alliance making to form any large nations.
Also, we do hear about Tuscon surviving the war. Raul mentions living there before the Legion came, and it was some sort of civilized town. Sawyer also mentioned the Legion doesn't destroy the civilized towns they come across, they just rule over them, though those people aren't considered part of the Legion. So we know there was a few of them spread across Arizona and New Mexico before The Legion came.