Sith

The Sith were an organization of of Force practitioners who trained themselves to use the Dark Side. They attempted to conquer the galaxy in the early days of the Galactic Republic, but they were eventually defeated, largely because of internal power struggles.

Rivalry among the Sith resulted in numerous murders among their ranks. They attempted to reduce the problem by working in small groups, eventually operating only in Master/Apprentice pairs. Even so, the entire Sith organization was reduced to just two members by the time of the Clone Wars, both of whom died at the Battle of Endor.