A long time ago, in a galaxy far, far away...
The Mandalorian Wars was one of the bloodiest conflicts in Galactic History. But it would only be a precursor to what would follow: the Jedi Civil War.
The Jedi who had taken the fight to the Mandalorians, after vanishing into the with their leaders Revan and Alek into Unknown Regions, return as Sith to conquer the very Republic they had defended. The generals who led them returned not as heroes, but conquerors -- re-christened as Darth Revan and Darth Malak, with a limitless fleet of alien ships and an ever-expanding army of Jedi turning to the teachings of the Sith and soldiers conscripting to their cause. Not even Darth Malak's betrayal of his master halts their advance, claiming Darth Revan's place for his own.
But unknown to the Dark Lord, Revan had survived her betrayal, saved by the leader of a Jedi strike team sent to capture the two leaders of the Sith -- a young jedi named Bastila Shan. With her identity and memories erased, Revan recovered the Star Maps leading to the Star Forge which had supplied the Sith with their endless armada... only to fall back into the Dark Side and draw Bastila down with her, the two of them claiming the titles of Sith Master and Sith Apprentice and not only killing Malak but destroying the heads of the Republic and Jedi leadership in one fell swoop, destabilizing what was left of the tattered Republic defenses and reclaiming the Sith under Revan's leadership.
However, right before the Galactic Republic and Jedi Order could be dealt the death-blow, Revan vanished without a trace, and the Sith Empire collapsed. However, the damage was already done -- Outer and Mid Rim had been devastated by the war. Countless refugees flee to other worlds, Nar Shaddaa in particular. The Jedi Order was left a shadow of its former self, with barely a hundred remaining who had survived and remained true to the Code. One such Jedi -- an Exile named Meetra Surik -- did much to help the Republic regain stability, only to vanish herself after the defeat of the monstrous Sith Lord Darth Nihilus over the world of Telos IV.
But now, after nearly thirteen years of absence, Darth Revan has once again returned -- at the head of a massive new Empire that far outstrips her original one in size, after having overthrown the prior Sith Emperor Vitiate and taken his place. Barely recovered from the nightmare of the past wars, the Republic is ill-equipped to deal with the resurgent threat of Revan, and an age of darkness seems to be fast approaching.