The most powerful factions fight it out, until just a handful are left. Nations like NCR take over most of North America. Same deal plays out all over the world. New Nations form and they form international trade once more. Super Mutants are long gone or super rare, the same with ghouls. As time goes by and nations form, humanity stays away from radiation, if there is any place still radioactive after all that time.
The Nations of the Earth do what they always do.. they start coming into conflict with one another. The most powerful try to force their influence on the weaker ones, and an arms build up happens. New technology is developed and old ones rediscovered and improved on. Possibly becoming more advanced then the pre-war world.
At some point, it all ends again in Nuclear War/Armageddon "War, war never changes." Humanity then once more has to slowly rebuild from the ashes.