Not Adventure Time world. Just the style. Braking the gaming fourth wall, NPCs are very aware of Adventurers, evil is very evil and obvious, good is very good and obvious, and all kinds of monsters and dungeons are everywhere.
In the great continent of Forlin a massive war had raged. Terrible monsters hailing from The Waists decimated cities, leaving ruins in their wake. Few civilized powerhouses were left and the war has subsided after the head of the snake was cut off.
In the rain shadow of The Impassable Mountains is The Great Forest, which is neigh impregnable. This Jungle, and it's beasts, holds the terrible evil at bay, though they could just sail across that Bay, if they could get organized again.
A large armed force protects the farm lands in northwest Forlin Plains, however the heavily fortified cities, with their stronghold walls, are a safe haven when the soldiers are not strong enough for bigger threats.
Trade has been slowed way down. The two major trades are wood and ore from the forests being sent to the north and the food from the north being sent to the south. Exotic trades are large investments, so items can come at a very high cost, if they are not made in their own town. This keeps mercenaries well employed, as well as the undertakers.
