I'd say Fallout 2 and 76 are the two games that have the narrative that deal with that stuff more directly as opposed to it being more hidden narrative. NV has it a bit but that's more to do with new factions rather than a global hegemony like the US.

76 even does the correct thing as well where, when the bombs hit, people are actually kind and helpful to each other with some exceptions. Oh, and the raiders in the game are (or descended from) rich assholes who were in a skiing resort when the world ended. The world only really falls apart due to the actions of a crazed anti-Communist and the scattered groups general distrust of each other, for varying reasons.