Other modes include a skirmish battle mode and multiplayer games. The game brought about several changes in gameplay, some introduced in Command & Conquer: Red Alert 2, including garrisonable structures, neutral tech buildings, unit upgrades and veteran levels, and special powers unique for each playable faction. The game's story sees the Global Defense Initiative and the Brotherhood of Nod engage in a new global conflict, this time as major superpowers, only for the war to attract the attention of a new extraterrestrial faction known as the Scrin, which attacks both sides while harvesting Tiberium for its own purpose. The game is a direct sequel to the 1999 game Command & Conquer: Tiberian Sun, and takes place roughly seventeen years after the game's expansion pack Firestorm, in which Tiberium has grown to become a considerable threat to the planet, leading to the world's political borders and territories being remade into zones denoting the level of contamination by the alien substance. Command & Conquer 3: Tiberium Wars is a 2007 science fiction real-time strategy video game developed and published by Electronic Arts for Windows, Mac OS X and Xbox 360 platforms, and released internationally in March 2007.