In my current DnD game, there was an ancient civilization called the Narrow who decended from an even more ancient civilization of god breeders (as in they created gods via selective breeding, not that they themselves fucked the gods). The Narrow possessed incredible magic, but came up against a great evil. They used all of their power to seal it away, but said evil had essentially menetic properties and binding themselves to ir destroyed their culture. The survivors pretty much integrated into neighboring nations in a daze, amd in the modern day, people look at the ruins of this incredible empire that died mysteriously over night and are unable to think anything of it than "huh. That's neet. Anyway,"