Command & Conquer 3: Tiberium Wars is a real-time strategy game developed by Electronic Arts Los Angeles for the Windows and Xbox 360 platforms, and is a sequel to the 1999 RTS title Command & Conquer: Tiberian Sun and its expansion pack Firestorm by Westwood Studios. Canonically it takes place at the advent of and during the "Third Tiberium War", after the Brotherhood of Nod launches an unexpected and worldwide offensive against the Global Defense Initiative, abruptly ending a period of seventeen years of silence and crippling GDI forces everywhere. With the odds tipped in Nod's favor this time, GDI field commanders rally their troops and begin to combat the Brotherhood's second re-emergence, trying to restore lost hope. The game also features the introduction of a new third faction (Scrin) to the Tiberian series of the Command & Conquer games, and is the second C&C title in which players are able to upgrade their forces.

Source: Wikipedia Article