Rule of Two
this was the name, used by the Jedi Order, to describe the basic tenet of the Sith, which was implemented in the wake of the Battle of Ruusan. Under the Rule of Two, there could only be two Sith in power at any time in the galaxy: a Master and an apprentice. Adherence to this rule would ensure that the Sith never became the greedy, power-hungry mob they were during the Light and Darkness War, but could grow strong in secrecy until they had enough power to take control of the galaxy.