The origins of the Rustamid state can be traced to the Berber Kharijite (Ar: Khawarij) revolt (739-772) against the new Arab Sunni power that was being established across North Africa following the Islamic conquest. Originating in Mesopotamia, the Kharijite movement had begun in protest against the fourth caliph Ali, who consented to negotiate during a Muslim civil war (656-661) despite his superior army in the field; as a result some of his armed forces left the camp, hence the movement of the Khawarij ["those who go out"]. Originally puritan in outlook, being of the ummah of Islam for a believer indicated a perfection of the soul, yet sin constituted a schism, a split from other believers, the sinner becoming an apostate. The leader must be above reproach, yet could be non-Arab. Never attaining lasting success, but persisting in its struggles, the Kharijite movement remains today only in its Ibadi branch, with small minorities in isolated locales throughout the Muslim world. The Ibadis predominate in Oman.