The Rule of Two (jan 1, 6689 – jan 1, 7958)

Description:

After orchestrating the complete annihilation of the armies of the Republic and all Sith at Ruusan, Darth Bane established his Rule of Two. Bane's philosophy established that there would only be two Sith at any given time, a Master and an Apprentice. Together the two would work in the shadows to manipulate the galaxy toward their ultimate goal, the destruction of the Jedi and the Republic.

It is speculated that Bane's Rule of Two may have had a secondary goal. Just as Vitiate before him attained a level of immortality through possession, limiting Sith to only two practitioners would have given Bane a path toward generational immortality. Whether this was attempted and failed however is unknown.