Fourth Great Schism

The Fourth Great Schism was a pivotal split among the ranks of the Jedi Order in 2000 BBY.

Around this time, a Jedi Master known as Phanius had abandoned the ways of the Jedi in pursuit of alternate teachings, leading him on a quest to revive the dark-side-worshipping Sith Order. By this point, the Sith were commonly believed to have been destroyed for centuries. The fallen Jedi Master proved otherwise, however, after seeking out a number of existing Sith clans throughout the galaxy. Assuming leadership over these clans, Phanius declared himself a Dark Lord of the Sith under the identity of Darth Ruin.

Prompted by the Dark Lord's ascension, fifty additional Jedi followed in Ruin's footsteps, leaving the Jedi Order in favor of his growing Sith empire. These events gave rise to the New Sith, initiating a thousand-year-long crusade—the New Sith Wars—against the Galactic Republic and the Jedi.

Text and facts from the “Fourth Great Schism” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.