Sarah knows the following:<br/><br/>The Tau are a xeno race who live on the other side of the galaxy, who specialize in subjugating and brainwashing other species to do their bidding.<br/><br/>Tau are shorter than humans, usually between 4 and 5 feet in height.  Their skin is a pale blue-grey, and their eyes are bulbous.  Their faces have no  noses, and they're quite often seen wearing full body exo-suits.   They are not particularly agressive, but their technology is highly advanced, and quickly evolving.  At present, the Tau have developed Space Marine level technology, and are only getting better, rapidly progressing towards Dark Age of Technology level science.  At present, Tau are classified as Xeno Exterminatus.  Humanity tried to destroy them in the Damocles Gulf crusade, and easily conquered their fleets, but was bogged down by their ground forces, and distracted by a Tyranid hive fleet.  The most recent crusade against the Tau, the Achilus Crusade, is in full swing, but, ironically, also disrupted by Tyranid intervention and mass chaos uprisings.<br/><br/>Tau do what they do because it is decreed by their leaders, the Etherial Caste.  They believe that their efforts contribute to a "greater good" and that by enslaving others, they create unity.  Even some humans have fallen under the sway of the Tau, and been made into cannon fodder for their armies.  Tau are the primary employer of the Kroot, though the Kroot seem to be getting the better of the arrangement for their own mysterious purposes.<br/><br/>In space, Tau use fleets of battleship sized ships escorted by a screen of hilariously weak cruisers and escort vessels carried aboard the battleships.  Most tau fleets have a tiny command vessel which coordinates the firepower of the fleet, making them very dangerous at long range.  In general, the Tau are very easy to destroy in space because their weapons can't penetrate heavy armor, and their ships are pathetically slow and not heavily armored enough.  On the ground, Tau have personal weapons of incredible power which use stable phased plasma, and artifically intelligent drones which support their armies.  Incredibly powerful flying tanks and mechnized battle-suits form the core of Tau military technology, and would almost threaten Space Marines if the Tau weren't so hopelessly inept at close combat.  Tau fight for the benefit of their race, rather than for hatred of their enemies, and cannot bear to kill them up close.  Such is their weakness, and why they will inevitably be ground under the heel of humanity.