Sith
The Sith are a group of force users who follow the dark side.
History
Around 7000 BBY, a group of Jedi became frustrated with the Jedi Order's limitations of Jedi teachings. They pursued knowledge the Jedi Council had forbidden. They also craved for power the light side of the Force could not offer them. These Jedi broke away from the Jedi Order.
The separation was violent. The former Jedi became infatuated with the dark side of the Force. They started ancient Sith rituals, applied Sith alchemy and created genetic mutations. They rejected the Jedi code of peace and serenity in favor for passion and strength.
Some former-Jedi became well known. One of these was Ajunta Pall a warrior of immense strength and ambition. Another was Karness Muur, a master of forbidden techniques. Next is XoXaan. XoXaan's knowledge of the dark side ran deeper than most could comprehend. These dark Jedi believed that conflict was the true path to power. A philisophy of only the strongest will rule emerged.
The philisophical divide between the Jedi and dark Jedi erupted into open warfare. This war is known as the Hundred Year Darkness. The destruction of the war became immense. The dark Jedi used their alchemy and force abilities to create mutations and creatures that would bring the Jedi to their limits. Around 6900 BBY, at the Battle of Corbos, the Jedi Order defeated the Dark Jedi rebellion. Once the Jedi claimed victory, they adhered to their belief of mercy. They exiled the Dark Jedi from the Republic territory.
Cast outside the Republic territory, these dark Jedi started exploring. They eventually found the remote world Korriban, the homeplanet of the primtive species, Sith Pureblood. The Sith Pureblood had a natural connection to the dark side of the Force, though believing it was only magic. The exiled dark Jedi saw an opportunity. They used their dark powers to awe the Sith people, presenting themselves as gods. The Sith Pureblood started to worship the dark Jedi. Eventually, the dark Jedi started to intermarry with the Sith Purebloods.
The strongest of the dark Jedi, Ajunta Pall, declared himself the first dark lord of the Sith. The dark Jedi then adopted the name of the Sith Pureblood, calling themselves Sith lords. The Sith lords under the dark lord of the Sith, formed the Sith Empire. The empire started to expand and they built large temples and academies on other planets to train large armies of Sith lords.
During this era of expansion, several Sith lords rose to prominence. Among the most feared was Tulak Hord, who subjugated several large systems. One of the planets he conquered, was Dromund Kaas, an important refugre for the Sith later.
Around 5100 BBY, the Sith Empire reached the golden age of the Sith. It came under the rule of dark lord Marka Ragnos. He maintained his position as dark lord for over a century. Under Marka Ragnos, the Sith Empire expanded it's borders and became immensely wealthy.
Approximately at 5000 BBY, Marka Ragnos died. His death caused a power vacuum to emerge in the Sith Empire. This power vacuum threatened all the growth Marka Ragnos had achieved. Two powerful Sith lords emerged as the primary contenders for his throne. The first was Naga Sadow, an ambitious and forward thinking Sith. He believed the Sith Empire should expand intensively and aggressively. The second was Ludo Kressh. Who believed to consolidate their power in their current systems and not to spread their forces thin.
Marka Ragnos's funeral became the stage of their rivalry to erupt. Initially, Sadow and Kressh had a verbal confrontation. However, this confrontation quickly turned into a duel between the two. A ghost of Marka Ragnos appeared and halted the duel, stating their rivalry would undo all the Sith's progress. The ghost dissapeared, and though the duel ceased, their rivalry was still at large.
Up to this point, the Sith Empire had grown through isolation. No Jedi knew of the existence of the Sith Empire. Both Sadow and Kressh started aligning themselves with various other Sith lords to be stronger than the other. The Sith Empire was at the brink of civilwar.