I distinctly remember that generally, once the oil ran out circa 2050, it started going to high hell. The European Commonwealth and the Middle Eastern Bloc or whatever went to war nearly exactly right quick, and there's no way the USA didn't feel the affects of that. The virus was hitting US cities, which always seemed to me to be the antithesis of all that 60s and 70s planning, from looking at the intro of Fallout 1 alone - less 'we did it guys!' and more 'Bees in a hive' or 'Ants in a hill' crowdedness and 80s level of violence already in full swing.
By the time of the Great War, the people alive would have had 20+ years of living in a collapsing world. Your mind can fill in the little details beyond the canon lore, but it was no where near pretty in any case; with the degradation of soft power for pure hard power, with hungry and scared kids joining the army just to have bread shooting down hungry and scared kids who don't want to join the army but still need to survive. The dreams of detente and prosperity have all been forgotten and it's either the US survives, or no one survives.
Then by 2077, the government has all but abandoned everything and everyone it doesn't consider salvagable; when Maxson rebelled no one came by to squash him - the guy who is guarding one of the most ambitious projects of the USA, who rebels, is allowed to go scott free. Similar incidents could had been expected for years beforehand and concurrent with his, and it points to a complete destruction of order within the government itself. From that, one can easily imagine how horrible life would be in the big cities by that time and the situation would be some kind of mix of Mad Max 1 and The Forgotten War (When Mendoza returns in 2029); and then someone sets off a first strike, and the missiles fly.
So, culture wise, it would be the darkest days of the 80s, really, for twenty years on end, from the top of the White House to the end of the alley in Brooklyn or Los Angeles; a society barely functioning on the best days and even then only due to the sole fact that the government looks your way because you're useful and there's still some good people trying to keep it all together; but even then they die off or run away or are broken down.