It sounds like a more extreme version of what happened to the Great Kingdom (and provinces) after the Greyhawk Wars. What are those aristocrat undead of Aerdy called? Animus or something. Anyway, I reckon that's an appropriate horse to back for such a kingdom if you're setting it post-wars.-The creation of a "Kingdom of the Undead", a plague-wasted land ruled by a chaotic "alliance" of Deathgod Cults, Lichkings and Vampiric Lords, only united by a common goal of bringing Death and Destruction across Oerth, but otherwise feuding amongst themselves, especially due to the conflicting influence of different Death Cults vying for dominance (Nerull vs Orcus, mostly). Generally, an excuse for using nearly everything out of Libris Mortis. Dunno where I'd put it, though.