Cannibals of the Great Wash
Humans live throughout the Northern Swamp of Kalerre, known as the Great Wash. A thousand years ago, mariners from the Northern Hemisphere were blown by a tremendous storm south to the Land of Kalerre. In later days, some said they were carried by the Lord known to the Wemics as Ice, but others said that He contrived to abduct them. In any event, these mariners landed in the Great Swamp, and they were met there by an old wise man. He invited them to a feast, and the food he gave them was spiced with Paradise.
Paradise is an herb with a flavor surpassing all flavors, next to which all other tastes are like dirt or sand. It varies from preparation to preparation, so that one needn't become bored, but even boring, Paradise defeats all else in taste as the noon sun defeats starlight. Paradise is not addictive, but after tasting Paradise only once, all other foods taste like stale bread and briny water forever after.
Paradise also has a happy side effect: a regular diet, rich in Paradise, prevents all disease and confers unnaturally long life. There are several unhappy side effects as well -- if a person who lives on Paradise gives it up, the person is more susceptible to disease for about a year, and tends to have the symptoms of a cold for the course of that year. And if a person gives up a diet rich in Paradise, the person becomes permanently sterile.
After ten or twenty years, humans become acclimatized to Paradise, and its taste begins to fade. The only way to revive the taste is to mix the herb in blood. After another ten or twenty years, only human blood will do. After another ten or twenty years, only raw human brain tissue will do.
As a consequence, the society that has developed in the Great Wash is primarily cannibal. And since human sacrifice and cannibalism is the norm, it is also evil and corrupt. People of the Wash have developed Dark Magics, and they view Wemics as their main enemies.