Having played New Vegas before I played FO1, this was very striking to me. In particular, I was really surprised at the way Shady Sands was portrayed in Fallout, and had a hard time linking it to the way the NCR appeared in NV. In fact, the way the NCR developed is probably my biggest gripe with the entire series.
To me, it just doesn't make sense that a tribal village with seemingly no old world knowledge and a unique culture and mythology (references to "Dharma", for example, which seem to have been dropped after FO1) would within a generation or two adopt the political and social structures of the Old World and do it in such a way that they appear like a continuation of the US government.
It doesn't make any sense because you associate Shady Sands with tribals. You missed the culture of the village when you played
Fallout 1 if you think that, since several of its inhabitants express very plainly that they don't like being looked down upon because they live in "mud huts". You can see the difference in culture from one person to the next if you compare a father with his own daughter, specifically Aradesh and Tandi. Aradesh appears to be almost stereotypically Indian while Tandi comes off as a very Sourth Californian Valley girl. Shady Sands is not a "tribal" culture as much as it is multicultural, and that was deliberate as part of the story/setting/plot. Later on in the game it's explained why, and elaborated upon in FO2 and the FO Bible: Vault 15's social experiment was cramming 1000 people of VASTLY different cultural backgrounds to see what would happen, what kinds of friction would arise between peoples of such drastically different background, and unexpectedly everything worked out for all of the occupants... Until the structural supports catastrophically failed and the Vault caved in (one of the game's many "dark humor" jokes, because the Vault Catalog so cheerfully assured that it was safe from any earthquake damage). The result of the Vault collapsing was the inhabitants fleeing into the Wasteland to form 4 separate groups: the raider bands the Vipers, Jackals, and Kahns, and the village of Shady Sands, the latter of which being the only "peaceful civilization" of the four.
So, as a result, Shady Sands was, like the Vault where its people came from, a very culturally diverse settlement, NOT "tribal". Like Vault City, Shady Sands was one of the few settlements founded by Vault Dwellers, so that's why, decades later, it erupted into a monolith of Old World power and values. Each game emphasized that the focal points of civilized advancement in the wasteland was always around some kind of "resource". In the Hub's case it was water, in Adytum's case it was the Vault they originated from, and in the Follower's case it was the library. Obviously Adytum was one of the more advanced settlements in FO1, the Followers were one of the most educated groups, and the Hub was the most prosperous place in the Core Region. Vault City would demonstrate 80 years later how advanced a settlement could be when it had Pre-War tech at its disposal from the Vault they emerged out of, so it shouldn't serve as any surprise that Shady Sands was no different. They WERE excavating Vault 15 resources up until a few months/years before the Chosen One's arrival, after all (which was only stopped because of the squatters keeping them away and the New Kahns orchestrating the whole thing), and on top o that they were being assisted by the Brotherhood in their technological developement.
Add to that the NCR was founded by Shady Sands but populated by several city states that were not Shady Sands, and you can clearly see why the NCR, generations later, seemed "so white". The PEOPLE always were, but the cultural center where it all started was much more diverse.