Kharijites opposed both 'Ali and Mu'awiya, and appointed their own leaders. They were decisively defeated by 'Ali, who was in turn assassinated by a Kharijite. Kharijites engaged in guerilla warfare against the Umayyads, but only became a movement to be reckoned with during the Second Fitna (the second Islamic Civil War) when they at one point controlled more territory than any of their rivals. The Kharijites were, in fact, one of the major threats to Ibn al-Zubayr's bid for the caliphate; during this time they controlled Yamama and most of southern Arabia, and captured the oasis town of al-Ta'if. The Azariqa, considered to be the extreme faction of the Kharijites, controlled parts of western Iran under the Umayyads until they were finally put down in 699 CE. The more moderate Ibadi Kharijites were longer-lived, continuing to wield political power in North and East Africa and in eastern Arabia during the 'Abbasid period. Because of their readiness to declare any opponent as apostate, the extreme Kharijites tended to fragment into small groups. One of the few points that the various Kharijite splinter groups held in common was their view of the caliphate, which differed from other Muslim theories on two points. First, they were principled egalitarians, holding that any pious Muslim ("even an Ethiopian slave") can become Caliph and that family or tribal affiliation is inconsequential. The only requirements for leadership are piety and acceptance by the community. Second, they agreed that it is the duty of the believers to depose any leader who falls into error. This second principle had profound implications for Kharijite theology. Applying these ideas to the early history of the caliphate, Kharijites only accept Abu Bakr and 'Umar as legitimate caliphs. Of 'Uthman's caliphate they recognize only the first six years as legitimate, and they reject 'Ali altogether. By the time that Ibn al-Muqaffa' wrote his political treatise early in the 'Abbasid period, the Kharijites were no longer a significant political threat, at least in the Islamic heartlands. The memory of the menace they had posed to Muslim unity and of the moral challenge generated by their pious idealism still weighed heavily on Muslim political and religious thought, however. Even if the Kharijites could no longer threaten, their ghosts still had to be answered. The Ibadis are the only Kharijite group to surivive into modern times. ibn Abdul-Wahhāb The 18th-century Islamic revivalist Muhammad ibn Abd al-Wahhab