- "The Fourth Great Schism, which occurred a millennium ago, brought on a thousand years of fighting, the ascendance of Darth Ruin and the Sith, and the plague that provided the drumbeat for what was truly the Republic's Dark Age. It was a military campaign that nearly brought an end to civilization."
- ―Restelly Quist's writings
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 chose to follow 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.
- Star Wars: Episode I The Phantom Menace novelization (First mentioned)
- Star Wars: Episode I The Phantom Menace unabridged audiobook (Mentioned only)
- Star Wars Episode I Journal: Darth Maul (Mentioned only)
- The Essential Chronology
- The New Essential Chronology (First identified as Fourth Great Schism)
- The Complete Star Wars Encyclopedia, Vol. III, p. 114 ("Ruin, Darth")
- Jedi vs. Sith: The Essential Guide to the Force
- The Essential Atlas
- The Jedi Path: A Manual for Students of the Force