This is the background to my current D&D project, a West Marches cover band cover band cover band. The prep started as just an exercise to do something in the vein of 'bog-standard D&D,' but I've ended up prepping enough material that I might as well post it in case I don't get to run it before my interest turns to something else. In a nutshell, the premise is to take the Keep on the Borderlands, and add approximately two centuries of settlement, plagues, invasion, decrepitude, and revanchism.
The Eastern Principalities were once the edge of the Realm of Man, the Old Borderlands between Law and Chaos, but rugged explorers and bellicose adventurers slew the orcs and goblins and worse who plagued its forests and swamps, and founded new towns and castles to bring the land within the orbit of light and reason.
But now, as war and rebellion engulfs the Realm of Man, the return of Chaos to the Principality of the Keep again draws grim adventurers to seek fortune …