Third Great Schism

The Third Great Schism was the second to last of the Great Schisms experienced by the Jedi Order.

History
In 4,250 BBY, during the Vultar Cataclysm, a Jedi civil war took place on Coruscant, after which the dark-siders involved fell back to the Core World system of Vultar. In the Vultar system they found ancient technology that lead them to believe the entire solar system had been artificially created. The dark-siders collected the ancient machines that they found, including the peculiar Cosmic Turbine, but were unable to control the devices. In the end, due to their own ignorance, the dark-siders ended up annihilating themselves and the entire Vultar system.

Behind the scenes
Since there was no information about the Third Schism in the article Evil Never Dies: The Sith Dynasties, this may indicate that the Dark Jedi in this conflict were not associated, or did not consider themselves Sith.