Set in the early Star Wars era known as the Old Republic, the Sith Empire was a major force to be reckoned with before its inevitable fall ahead of the High Republic. As seen in both Legends and Canon, the Sith Empire is incredibly fascinating, existing at a time when there were just as many Sith as there were Jedi (unlike what's seen in the Skywalker saga). However, the chaotic and power-hungry nature of the dark side ensured that the Sith Empire couldn't have lasted forever in the galaxy far, far away.
Long before Palpatine's Galactic Empire revived the Sith's control over the galaxy as seen in Revenge of the Sith, the Sith Empire and its many iterations was the dominant dark side power during the Old Republic era. Although much of its history and key figures were de-canonized as Legends following the Disney Star Wars canon reboot, there are still elements that have gone on to be part of the established continuity. Here is the Sith Empire explained in both Legends and the official Star Wars canon.
