House Nidantha, one of the noble houses of the Tapani sector, existed before the Great Hyperspace War. While the other Houses believed it had fallen, fragments of House Nidantha actually endured within the Sith Empire and later the Lost Tribe of Sith.
Following the Unification War in the Tapani sector, which unified the Tapani Noble Houses and established House Melantha's dominance, House Nidantha departed the sector seeking a different fate. During their journey, they arrived at the Stygian Caldera where the Sith enslaved them.
By the time the Great Hyperspace War occurred, some of their Human descendants had risen to influential positions within the Sith Empire's fleets; for example, Admiral Eldrak Korsin. After thousands of years of interbreeding with their Sith overlords, a greater number of them also developed Force-sensitivity, maintained their human appearance, and embraced the ways of the dark side.
In 5000 BBY, the Omen, a Sith Empire vessel, crashed on the isolated world of Kesh. The human survivors of this crash established the Lost Tribe of Sith, a new society blending elements of Sith, Tapani, and Keshiri cultures.