<P> With the Buyid dynasty on the wane, a vacuum was created that was eventually filled by the dynasty of Oghuz Turks known as the Seljuqs . By 1055, the Seljuqs had wrested control from the Buyids and Abbasids, and took any remaining temporal power . When the amir and former slave Basasiri took up the Shia Fatimid banner in Baghdad in, the caliph al - Qa'im was unable to defeat him without outside help . Toghril Beg, the Seljuq sultan, restored Baghdad to Sunni rule and took Iraq for his dynasty . </P> <P> Once again, the Abbasids were forced to deal with a military power that they could not match, though the Abbasid caliph remained the titular head of the Islamic community . The succeeding sultans Alp Arslan and Malikshah, as well as their vizier Nizam al - Mulk, took up residence in Persia, but held power over the Abbasids in Baghdad . When the dynasty began to weaken in the 12th century, the Abbasids gained greater independence once again . </P> <P> While the Caliph al - Mustarshid was the first caliph to build an army capable of meeting a Seljuk army in battle, he was nonetheless defeated in 1135 and assassinated . The Caliph al - Muqtafi was the first Abbasid Caliph to regain the full military independence of the Caliphate, with the help of his vizier Ibn Hubayra . After nearly 250 years of subjection to foreign dynasties, he successfully defended Baghdad against the Seljuqs in the siege of Baghdad (1157), thus securing Iraq for the Abbasids . The reign of al - Nasir (d . 1225) brought the caliphate back into power throughout Iraq, based in large part on the Sufi futuwwa organizations that the caliph headed . Al - Mustansir built the Mustansiriya School, in an attempt to eclipse the Seljuq - era Nizamiyya built by Nizam al - Mulk . </P> <P> In 1206, Genghis Khan established a powerful dynasty among the Mongols of central Asia . During the 13th century, this Mongol Empire conquered most of the Eurasian land mass, including both China in the east and much of the old Islamic caliphate (as well as Kievan Rus') in the west . Hulagu Khan's destruction of Baghdad in 1258 is traditionally seen as the approximate end of the Golden Age . Mongols feared that a supernatural disaster would strike if the blood of Al - Musta'sim, a direct descendant of Muhammad's uncle Al -' Abbas ibn' Abd al - Muttalib, and the last reigning Abbasid caliph in Baghdad, was spilled . The Shiites of Persia stated that no such calamity had happened after the deaths of Husayn ibn Ali; nevertheless, as a precaution and in accordance with a Mongol taboo which forbade spilling royal blood, Hulagu had Al - Musta'sim wrapped in a carpet and trampled to death by horses on 20 February 1258 . The Caliph's immediate family was also executed, with the lone exceptions of his youngest son who was sent to Mongolia, and a daughter who became a slave in the harem of Hulagu . </P>

Describe the abbasid method of ruling their empire