Dread Masters crisis

The Dread Masters crisis sparked due to the Dread Masters' escape from their imprisonment on Belsavis and their ambition to achieve total dominance. The Dread Masters' were freed around 3641 BBY and returned to Imperial service; the Sith Emperor's death in the battle on Dromund Kaas prompted them to enact their own plans separate from the Sith Empire. This resulted in several battles that pitted both the Empire and the Galactic Republic and the Jedi Order against them; the Dread Masters' forces were thwarted on several occasions and forced them to settle on Oricon for a final offensive.

The Republic and the Empire formed a brief truce in order to confront the Dread Masters' after the latter used the Force to influence both sides' minds to drive them insane. But ultimately an offensive on Oricon resulted in the Dread Masters' deaths save one that the Republic captured for treatment with the Jedi.

The end to this conflict meant that both sides could focus their resources on the war since the Dread Masters' threat forced a brief stop to both sides' offensives.

Text and facts from the “Dread Masters crisis” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.