The Great Sith War was a conflict fought between the Jedi Order and Sith prior to the Great Hyperspace Disaster. According to Jedi Master Oppo Rancisis, the Jedi won the war. In 232 BBY, Rancisis cited the Jedi’s victory in the war during a Jedi High Council debate over whether the Order was obliged to assist the Republic Defense Coalition in hunting down the Nihil raiders. Ultimately, the vote was narrowly decided in favor of Jedi participation, leading to the Battle of Kur.
The Great Sith War was first canonically mentioned in the 2021 novel The High Republic: Light of the Jedi. In the Star Wars Legends continuity, the Great Sith War was a conflict in 3996 BBY between a Sith faction headed by Exar Kun and an alliance of the Galactic Republic and Jedi Order.