During the war, moreso than ever before, was the art of necromancy used to its foulest. Druids could target immense areas of land, but the clever necromancer could easily target large populations in entirely different ways. And they did so with terrifying effectiveness. Many peoples used these arts during the war, but the ones who were the most prevalent in the use of necromancy were the Giants, the Illithids, and the Humans. After the war, the Mind Flayers became their own problem, and the Giants were by far the most weakened by the Maelstrom, to the point that those who took such actions in the war were not differentiated from the rest.
The humans who had taken part in such actions, however, were returned to their peoples, their homelands, and received in ways they did not expect. People who had been treated as heroes, who struck great blows against human enemies were treated with fear, or even revulsion for the manner of their victories. Some were even tried for their actions, even some who had been ordered to take those actions by the governments who now tried them. The most common sentence of such trials was exile.
The unwanted humans who had been necromancers during the war, whether they traveled due to a willing exile, or an imposed one, gradually started to find one another, and settle together. The only place that had been designated as human lands, but was not claimed by any country, became their homelands. Unfortunately, the land being unwanted was for much better reasons than its wanton settlers.
The Barrens was the name of that land at the time. For that is what its was. Mountains and hills, too rocky for most roots, with soil that would not sustain most vegetation. Creatures were sparse, and most plants that pervaded there were more likely to eat the settlers than be eaten.
After years of struggling to adapt, or at least survive, these survivors started to discover the waxing return of magic. Those that first noticed this quickly formed into "noble" houses, and using the arts of the ancestors that first settled the area (the necromancers of old), proceeded to 'augment' themselves to better survive the area.
But survival for the rest of these peoples was still a trial. So the noble houses set forth means to pacify their dangerous environment, and make it so that the populace would endure... permanently.
No-one knows just what was done, but most know to stay away from those lands these days because of it. Somehow, the land itself brings harm to those who walk upon it, sapping their health, and every so often, the air seems to pulse with energies that will crush the soul itself.
The population is now entirely comprised by various forms of undead, with the lowest cast being those of the Necropolitans. Though others, such as the Dread Warriors, are only a higher cast in name and station, seeing as how the Necropolitans are at least allowed their freedom to pursue their desires, as opposed to serving the noble houses in various ways. Only a very few, a chosen and select few, are chosen to be admitted into a Noble House, who are bound together by their new form, not by their old blood.
Noble Houses: Fatas (
Forged Ghosts), Alucious (
Vampires), Vimort (
Liches). There are others, but it is these three who lead, both in power and in numbers. Vimort being the smallest of the three, but by far more powerful, politically and otherwise.
DM Note: As far as the three undead I linked for the noble houses: Liches actually come in three varieties, MM, Dr, and Osle's and any of the three are permitted into House Vimort; Vampires only come Osle-style; Ghosts come in either MM style or Osle's, but only the Forged, or Created Ghosts, are permitted into House Fatas.