The Tau are a young race of alien humanoids from the Eastern Fringe of the galaxy who have created a rapidly expanding interstellar empire with highly advanced technology in only a few Terran centuries. Led by the mysterious Ethereal Caste, the Tau are compelled by their pseudo-religious philosophy known as the Greater Good to expand their borders until they have assimilated and imposed their collectivist ideology upon the entire galaxy. Unique amongst the other major intelligent races of the Milky Way, the Tau Empire effectively employs a combination of diplomacy and measured military force to acquire other intelligent species as allies to their cause. Though barely a blip on the galactic map when compared to the vast interstellar territories that encompass the Imperium, the Tau Empire poses a realistic threat to seize the frontier of space away from Mankind if something is not done to counter their continued expansion. Even many human worlds of the Imperium have found the Greater Good an attractive enough philosophy to turn their back upon the dictates of the God-Emperor.