One year after the end of the Mandalorian Wars, Revan and Malak returned at the head of a massive invasion fleet. Revan had fallen to the dark side, and assumed the title of Darth Revan, Dark Lord of the Sith… the great hero of the Republic had become a brutal, conquering Sith Lord.
—Dorak
Darth Revan's Sith Empire was an empire established by the Sith Lord, Darth Revan, and his apprentice, Darth Malak, in order to conquer the Galactic Republic, and replace it with their own regime.
However, after Revan redeemed himself and slew Malak, their Empire disintegrated, splitting into factions, and lasting until 3,915 BrS, when it finally dissolved.