IIRC in 40k Nurgle became a great power during the Black Death. In fantasy idk the origins but the chaos wastes where chaos is strongest are at the poles. The world map is literally just the real world with a bit of fantasy stuff like elf atlantis, and the landmass that would be "Britain" is Albion, a land of swamps and brutal savages. Culturally, Bretonnia is like a 50/50 of Britain/France with chivalrous knights and super poor peasants, where the peasants are tithed literally more than 100% of their harvest.