The conflict between the Jedi and Sith is central to the Star Wars universe, however, a similar rivalry occurred with another dark-side cult before that. The Jedi and Sith often represent the battle between the light and dark sides of the Force, but given the Order's 25,000-year history, it makes sense for the Jedi to have fought other groups before the creation of the Sith. The Star Wars books and comics have explored other dark side groups before in every part of the timeline, only now it's confirmed which of them came first. This revelation makes clear that the Sith weren't the first darkness the Jedi unleashed on the galaxy.
Star Wars: Timelines from authors Kristin Baver, Jason Fry, Cole Horton, Amy Richau, and Clayton Sandell sheds new light on the galaxy's history. It provides specific dates for the entire Star Wars timeline, which includes an overview of the Dawn of the Jedi and confirmation of when the Jedi's first dark-side enemies emerged. It also affirms that this splinter group predated the emergence of the Sith, something that was largely shrouded in mystery in other Star Wars media. While much is still unknown about the Jedi's first dark-side rivals, Star Wars: Timelines does reveal new information about them in relation to the Jedi Order's beginnings.
The Ordu Aspectu Predated The Sith 
Star Wars: Timelines reveals that the Order Aspectu, a splinter group of the Jedi Order, existed in 20,000 BBY. This dates them approximately 5,000 years after the Jedi Order was founded and 15,000 years before the Sith also splintered from the Jedi. The Ordu Aspectu, therefore, was the first confirmed dark-side cult that the Jedi fought and the first darkness they unleashed on the galaxy. That alone is a major reveal for the Star Wars canon timeline, but the fact that it happened so long ago puts the Jedi's conflict with the Sith into perspective, showing that they're only a small part of a much larger history.
