Age of Empires II: The Age of Kings (often shortened to The Age of Kings, "AoE II", or AoK) is a real-time strategy (RTS) video game developed by Ensemble Studios and published by Microsoft. Released in 1999 for the Microsoft Windows and Macintosh operating systems, it was the second game in the Age of Empires series. An expansion, The Conquerors, was released in 2000. A PlayStation 2 version was released by Konami in 2001, and a Nintendo DS spinoff, Age of Empires: The Age of Kings was developed by Backbone Entertainment in 2006. The Dreamcast port, by Konami, was canceled. The Age of Kings is set in the Middle Ages and contains thirteen playable civilizations. They are the Britons, Byzantines, Celts, Goths, Teutons, Franks, Mongols, Chinese, Japanese, Persians, Saracens (Arabs), Turks and the Vikings. Players aim to gather resources, which they use to build towns, create armies, and ultimately defeat their enemies. There are five historically-based campaigns, which constrict the player to specialized and story-backed conditions. There are three additional single player game modes, and multiplayer is supported.