In the aftermath of the Hundred-Year Darkness, the Sith returned to known space after many years to make war on the Old Republic and the Jedi Order—the ancient enemies of the Sith. For millennia both factions fought against one another, and periods of constant warfare ultimately strained the Old Republic’s resources. With the steady collapse of the Republic at hand, the Sith ultimately became the dominant power in the galaxy for a period of time.
During the Sith’s reign, a cult known as the Ascendant worked under the Chadra-Fan Miril and attempted to replicate the effects of the Force through technology. Although the group flourished during the era, the Ascendant was in fact opposed to the Sith and hoped to use their technology against the dark side users. However, the Sith declared their work to be blasphemous and dispatched the Darkseekers to destroy the cult. In time, the Sith found the Ascendant’s main temple and cut down its members, but Miril gave her life to ensure they would not take the Spark Eternal for themselves.
The Sith’s rule across the galaxy would ultimately decrease over time. Although the Republic still continued to fall, the Jedi and remnants of the Old Republic would have one final war against the Sith, bringing an end to their despotic reign once and for all, although the Order survived in secret through the Rule of Two.
One thousand years later, Supreme Chancellor Sheev Palpatine of the Galactic Republic, who was secretly the Dark Lord of the Sith Darth Sidious, transformed his government into the Galactic Empire, declaring himself Emperor in the process. He was an admirer of the Sith Empire and the Sith Lords who ruled it and wished to usher in a renewed period of its rule. He also possessed various artifacts dating back to the days of the dark empire.