Suel Imperium
The Suel Imperium was the original empire of the human ethnicity known as the Suloise on the Dungeons & Dragons world of Greyhawk. Decadent and cruel, being basically fantasy Nazis (the Suloise even look kind of like Nazi Aryan propaganda; pale skin, violet/blue/gray eyes, blonde or red hair), the Imperium subjugated all non-human races and non-Suloise humans it could get its hands on. This ultimately led to a powerful war with the Baklunish, a race of Arabian-featured humans, that culminated in the Imperium's destruction by the Rain of Colorless Fire, reducing its heartland to a barren waste called the Sea of Dust and scattering the survivors far and wide.
The Scarlet Brotherhood is a surving offshoot of the Imperium which has basically learned nothing from their ancestral destruction.