World of Warcraft (commonly known as WoW) is a pay-to-play massively multiplayer online role-playing game. It is Blizzard Entertainment's fourth game set in the fantasy Warcraft Universe, first introduced by Warcraft: Orcs & Humans in 1994. World of Warcraft takes place within the world of Azeroth, four years after the events at the conclusion of Blizzard's previous release, Warcraft III: The Frozen Throne. Blizzard Entertainment announced World of Warcraft on September 2, 2001. The game was released on November 23, 2004, celebrating the 10th anniversary of the Warcraft franchise. Although its initial release was hampered by server stability and performance issues, the game became a financial success and the world's largest MMORPG in terms of monthly subscribers. On July 24, 2007, Blizzard announced that the user base for World of Warcraft had reached a new milestone, with 9 million players worldwide. There are more than 2 million players in North America, 1.