Random campaign setting idea from work today, geared towards Lamentations of the Flame Princess and episodic play:
Sinkholes erupted across the Isles, swallowing small towns and ripping apart fields and forest. Things, unspeakable horrors born from God alone knows what Hell, crawled out of these holes to prey on men. The Catholics blamed the Protestant heresy for this eruption, while the Protestants blamed Catholic corruption. Parliamentarians and Royalists blamed each other, claiming the eruption as a sign of divine displeasure with their opponents. The monsters didn't seem to discriminate.
A generation passes. The British Isles are quarantined by the rest
of the world, and have become a bombed out, Balkanized hellhole crawling with demons and cultists, dwindling strongholds held by desperate bands of survivors surrounded by miles of scorched earth and ruined buildings. People have lost faith in the religions of their forefathers, and the only "Church" to be found is that of the Order of the Knights of St. Hopkins, Witch-Slayer, whose fanatical inquisitors' holy books seem to contain only verses on war and bloodshed. Warlocks and necromancers ply their foul trades openly, and every man strong enough to wield a sword or a pike does so.
Central authority (other than that of the Hopkinites) is nonexistent, with the ruined remains of cities squabbled over by various petty warlords and bandit kings. The savaged land between the cities is roamed by gangs of mercenaries, as well as both the monsters and those who seek to slay them. This once-green and pleasant land is now the playground of horrors both inhuman and all-too-human, and is a place where those with determination and strength of arms can become kings by their own hands.
In short: WITCHFINDER GENERAL meets MAD MAX in Mordheim.
Inspirations: WITCHFINDER GENERAL (Vincent Price's best role, if you ask me), ENEMY AT THE GATES, Sergio Leone's Dollars trilogy, Dennis Wheatley novels, Trey's Apocalypse Underground campaign musings.