I ran a game based on a crossover of Fallout and D&D, using 4e D&D rules. Take one magical utopia, applynuclear weaponsmegaspells, leave to stew for 200 years. The plot was actually inspired by Fallout Equestria, and the game was also influenced by my decision to set it in North Queensland, because I didn't want to draw my own map. For example there's a town there named after Proserpina so I needed to add a new deity to be the consort of the Raven Queen.
The war was between the human/dwarven alliance and the elves, and vaults were demiplanes designed to fit the village archetype of fantasy stories. The players fought slavers, undead, left over superweapon angels, angry fey, and a whole bunch of mutated creatures, like owlbears and three headed dragons. Well, technically they didn't fight the three headed dragon, they ran away like sensible people and collapsed a vault on it. They ended up resurrecting the god of peace, breaking one of the core tenants of the setting, that "War, war never changes" and winning the game.
That makes a scary amount of sense.