Burning Crusade

The Burning Crusade is a vast war of destruction with the goal of razing every world that had been ordered and shaped by the ancient Titans. It is a great war that rages beyond the ken of normal mortals. The universe houses innumerable worlds, and the Burning Legion currently invades a handful of them. Most mortals are blind to this secret conflict, but the wisest and strongest know of it - and some are heroes and leaders in this war. Champions from Azeroth and many other worlds battle across the cosmos, attempting to drive back the Burning Legion and keep the embattled planets safe from demonic corruption. Theirs is a desperate, epic war, and they welcome any who would join them. Beings of all sorts join forces - humans and draenei fight alongside orcs, high elves alongside night elves. Old rivalries are thrown aside in the face of the ominous legion. All who fight this secret war know that, despite the posturing and ambition of individual demon lords, Kil'jaeden was always Sargeras' second. He is the Legion's true leader. Out in the Great Dark Beyond, Kil'jaeden waits as demons and mortals die, biding his time for his minions to grow strong once again
WoWWiki:Burning Crusade