What was the first expansion pack for World of Warcraft?

The first expansion pack for World of Warcraft was The Burning Crusade.

Released in January 2007, The Burning Crusade raised the level cap from 60 to 70 and opened the portal to Outland, the shattered remains of the orc homeworld Draenor. Its story centered on the Burning Legion, Illidan Stormrage, and the campaign against demonic forces beyond Azeroth.

The expansion also added the Draenei and blood elves as playable races, flying mounts in Outland, new dungeons and raids, and the arena PvP system. A common mix-up is confusing it with Wrath of the Lich King, which was the second expansion and followed it in 2008. Cataclysm and Mists of Pandaria came later.