not include members of the main, sedentary body of the Muslim population, led to increasing instability as rival groups fought to control the organs of the state and regional commanders became de facto rulers in their own right.
The other major cause of instability in Islam, was the Shi'i-Sunni split. Under the Buyid rulers in Baghdad, 'Twelver' Shi'ism--the belief in the twelve imams (teachers) of Islam beginning with the cousin and son-in-law of Muhammad, 'Ali--began to take on the form of a political movement as well as a religious faction. Its adherents denigrated the memory of the first two caliphs, developed their own festivals on the days commemorating the murders of early Shi'a leaders, and began to venerate the tombs of members of 'Ali's family. They were particularly strong amongst the merchant groups in Baghdad. The caliphs, however, continued to follow the Sunni form of Islam and to emphasize their devotion to the memory of the early followers of the Prophet and the first four caliphs. The early years of the eleventh century saw a revival of Sunni influence in the city, with the caliph's refusal in 1003 to recognize a prominent Shi'a as chief judge and the employment of the strongly Sunnite Turks in positions of military influence. Such were the tensions caused by the growing hardening of attitudes, that when, in 972, an army was raised to march against the Byzantines, it was diverted by its Turkish commander to attack the Buyids and their supporters even before it had left Baghdad.
Thus even before the Turkish invasions of the eleventh century, the world of Islam was a divided one. Two caliphs with their own administrative structures lay at the centre and a host of lesser states, such as those of the Hamdanids of Aleppo and Mosul, the minor families controlling the coastal cities of Palestine, the Kurds of the regions south of the Caspian, and the Bedouin dynasties of the Syrian desert lay at the periphery. It was against these furthest outposts of Islam that the Christians of Byzantium and the west first came into conflict, and the inability of the caliphate to provide military assistance to them was one reason for the successes of the Byzantine state in the tenth century and the First Crusade in the eleventh. The
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