"Reign of Chaos" is a term often associated with the World of Warcraft universe, specifically referring to the expansion titled "The Burning Crusade." This expansion introduced players to the shattered world of Outland, where they faced new challenges, quests, and enemies. It marked a significant evolution in gameplay, offering new races, classes, and a higher level cap. In a broader context, "Reign of Chaos" can also refer to the Warcraft III game, which features a storyline centered around the conflict between various factions, including the Horde, Alliance, and the undead Scourge. This game laid the groundwork for many elements seen in later expansions and the overall lore of the Warcraft series.