The World Born Dead
The two ways this could end
Triumph of the Necromancers: Endless Night
Life sucks when the ravening horde of Wights and Shadows overruns your kingdom. In fact, life probably doesn’t even exist. Those that survive will normally have done so by taking shelter in small hallowed areas that the undead will not enter. But here’s the exciting part: once all life is gone in the region, the Wights can’t replace themselves. Sure, if you start with one Wight and then every day every Wight makes another Wight you’ll have an army one million strong in 3 weeks – but that’s already happened. They won, and now the Undead are on the down slop of the Spawn cycle. It’s really ugly, but you can retake the world. In fact, you’re probably going to. Necropoly isn’t really a government that lasts all that long in most D&D settings.
So here’s how it works: you spend your time in the hallowed grounds biding your time. Then, you come out and kill a couple of undead beasties. Then, the various Necromantic Intelligences that have sprung up will direct undead soldiers to go get you, so you’ll retreat back to the protected zone. Then you rinse and repeat. It’s like a high fantasy post-apocalypse world. As long as you remember that you’re small and furry and have to stay out of the way of the dinosaur zombies, you’re capable of chipping away at the onyx gauntlet that grips your kingdom.
Defeat of the Necromancers: Resource Rush!
OK, what does a necromantic army do to the land it passes through? Well, for staters it kills everything. Everything. That means that it leaves only the inanimate stuff behind. The soil, the houses, the gold, that sort of thing. In short, if you come in there with some seeds and some dreams after the necromantic army has been destroyed (and remember, many necromantic armies fight to the last), there is a bunch of livable land with no occupants and no monsters.
That is comedy gold right there, and every group of humanoids in the area is going to send all their second sons off to go try to colonize. That means that you have extremely mixed race settlements in the newly opened region. Gnolls live right next to Gnomes for reasons other than alphabetical assignment. But other than getting to live in the newly opened Oklahoma Territory with a bunch of radically different sapient species who don’t speak the same language or get along, remember that the monsters are coming back as well. This is empty land, so the monsters going in are doing so at a rate literally infinitely faster than the rate of monsters going out. Sure, it may be a trickle, but it’s completely asymmetric. When a displacer beast comes in to the region, it won’t have any of its normal food sources or enemies available – so it’s just going to go straight for the villages.
So while the monster presence in the area is almost insanely low by D&D standards, all of the monsters are going to immediately attack humanoid settlements as soon as they show up. That really makes it easy to DM, let me tell you.