The Blackfire Cabal was a somewhat diabolical evolution of the Fire Clan. After experimenting with the deeper concepts of elemental fire, they discovered they could manipulate it into something known now as Blackfire. Instead of being frightened by the destructive power, they embraced it and launched a campaign against their friends and neighbors.
They forcibly absorbed or destroyed other fire magic users, then turned their attention to the nearby Iron Clan of the Dwarves in the Dragonspine Mountains. Iron Clan was quickly forced to flee their home before the new might of the Blackfire Cabal.
The Cabal was eventually destroyed by "The Four" (Thistle, Jesram, Anther and Iluranel), a team of determined and capable Warrior Mages that had learned how to wield the Void as a weapon against Blackfire. They hunted down individual Blackfire mages and eventually destroyed the home base of the Cabal on the Plains of Salt.