A Sith Empire was an Empire (duh) ruled by a Sith Lord (double duh...). Sith Empires were the second most powerful thing in the universe. The most powerful thing in the universe is, was, and will always be, the Sith. But, that would actually make Sith Empires the most powerful thing because they're made up of Sith... oh, my brain hurts...
There were many different Sith Empires during Galactic history, but only a few of them were actually successful in becoming huge, powerful and notable empires, most of them were just two or three planets ruled by a Sith with delusions of grandeur. More notable (and successful) Sith Empires included Darth Darth Binks's Sith Empire and Palpatine's Sith Empire.
According to Sith law, every Sith Lord could claim a piece of space that was not yet claimed by another Sith and create their own empire in this region. However, they'd have to conquer the local population first. If they claimed a part of space that was already claimed by another Sith, or by the Jedi or some other group of hippies, they'd have to challenge their rule and fight a, usually, long and bloody war in that region. So most Sith claimed a relatively uninhabited part of space to prevent having to fight for it. They would usually set up an empire, build a huge army of mindless minions, and then go challenge some other Sith Lord or group of hippies.
Notable Sith Empires
As mentioned before, Palpatine's Empire was one of the most notable and successful Sith Empires. During the days of the cowardly Republic a Sith Lord name Sidious pretended he was an old, harmless and peace loving senator for the even more harmless and more peace loving planet of Naboo. Once he had gotten rid of the Supreme Chancellor he got elected to be the next Supreme Chancellor. Palpatine was actually so evil he could do all of this without the Jedi realizing he was an evil Sith Lord plotting to take over the Republic, in fact, he was so evil that at times he himself did not know he was plotting to take over. But in the end he remembered his plan, seduced Anakin Skywalker, turned him into Darth Vader and had him brutally rape and murder all Jedi. He then reformed the Republic into a Sith Empire which lasted until Luke Skywalker tricked Vader into killing Palpatine. While the Republic had lasted for hundreds of thousands of years, Palpatine's Empire only lasted little over twenty years. Alas, this was the sad story of many Sith Empires. The Sith would work hard to conquer a piece of the galaxy that had been ruled by peace loving hippies for many years, building a Sith Empire, and see it fall apart in a few years or so. Still, Palpatine's was one of the most successful.
Darth Elmo's Empire
Darth Elmo's great Sith Empire consisted of 8 habitable planets and many, many more destroyed planets. This was due to Elmo's favorite hobby, Destroying planets. It took Elmo many years to build his empire and he took great pride in finding as many different ways to destroy a planet during those year. Which is part of the reason why the empire consisted of only 8 habitable planets and hundreds of destroyed planets. Darth Elmo's Empire was eventually taken over by Darth Elmo after he had defeated himself in a lightsaber duel. The Empire was then taken over again moments later, this time by Elmo's Apprentice Dearth Nadir, because Elmo had (as mentioned before) killed himself during a lightsaber duel between him and himself.
Darth Darth Binks' Sith Empire
Darth Darth Binks' Sith Empire was probably the most successful Sith Empire in the history of the Sith. Darth Darth Binks did not only rule his own massive galaxy wide Empire, he also helped other Sith build theirs. Darth Darth Binks was the Supreme Sith of his time, the ruler of all Sith. His Empire, and the empires of his vast army of apprentices, drove away and replaced the rule of the Jedi and the hippies thought the Galaxy. Binks ruled his empire with an iron fist, after he had lost his hand a duel and had it replaced by a metal one. Binks' empire still threatens Galactic peace today and will continue to do so for many more years.
Sith Empire may also refer to: