Most messed up society in fiction

[The Overlord]

What are the most messed up fictional societies?

I think the Skeksis from the Dark Crystal are pretty awful, their casual cruelty, depravity and willing to commit genocide to serve their selfish ends is pretty damning.

The Dominion from Star Trek Deep Space 9 is pretty awful, they created a drug-addicted slave race like the Jem'Hadar and infected a planet that defied them with a plague that was passed down from generation to generation.

I also heard Warhammer has some pretty messed up societies.