At some point in time, the clans transitioned from serving to the people to pledging themselves to individual lords who were nominally representatives of the people and the Empire. With the reunification of the Empire in the wake of the Sith rebellion, some Jedi knights were elevated to lordship, becoming Jedi lords governing territories as well as clans. The practices of the Jedi clans became the only permitted school of thought regarding the Force. The Empire and the clans attempted to eliminate other orders that viewed the Force in ways that were contrary to the Jedi, especially the Sith. Only the Jedi were allowed to own kyber crystals, which were used to power the lightsabers wielded by Jedi knights.