The Jedi Civil War began in 3959 BBY and ended in 3956 BBY. Two prominent Jedi Knights Raven and Malak pursued enemy forces into deep space at the end of the Mandalorian wars. There on Dromund Kaas they found the True Sith Emperor. A short time latter they both returned to the galaxy as Sith Lords to make way for the true Sith Emperor's Return.