World of Warcraft: The Burning Crusade

The expansion's name marks the return of the Burning Legion — the vast demon army that ranks among the Warcraft universe's greatest threats, whose last invasion was turned back in Warcraft III: Reign of Chaos. This Legion and its allies are the central enemy players face in The Burning Crusade. Alongside some new regions on Azeroth, the expansion is centered on the ravaged, otherworldly realm of Outland, which the Legion and other powerful beings now control. When the Doom Lord Kazzak reopened the Dark Portal to Outland, the demons of the Burning Legion came flooding into Azeroth, and expeditions from the Horde and Alliance — reinforced by their new blood elf and draenei allies — passed through the gateway to stop the invasion at its source. On Outland's desiccated Hellfire Peninsula, the Alliance found heroes who had crossed over years before, while the Horde made contact with the Mag'har, the "uncorrupted" orcs who never took part in their race's original invasion of Azeroth. The expedition drew both factions deeper into conflict with the agents of the Legion and the lieutenants of Illidan Stormrage, who had claimed the shattered realm as his own.