Nerath
Nerath is the ancient human empire that most recently ruled a significant chunk of the known world in the Nentir Vale setting of Dungeons & Dragons. It was destroyed by hordes of gnolls, orcs and demons led by the White Ruin, a Half-Fiend gnoll champion of Yeenoghu.
Before its downfall, Nerath was an incredibly advanced society, to the point that warforged are actually native to the Nentir Vale setting because of the last two kings of Nerath.
Dragon Magazine ran two article series relating to Nerath. The first, "Guilds & Groups", focused on various NPC organizations that had their roots in Nerath and which had survived its fall. The second, "Nerathi Legends", fleshed out Nerath's neighbors and rivals, further padding out the lore for the Nentir Vale setting.