<P> The center of the Islamic Empire at the time was Baghdad, which had held power for 500 years but was suffering internal divisions . When its caliph al - Mustasim refused to submit to the Mongols, Baghdad was besieged and captured by the Mongols in 1258 and subjected to a merciless sack, an event considered as one of the most catastrophic events in the history of Islam, and sometimes compared to the rupture of the Kaaba . With the destruction of the Abbasid Caliphate, Hulagu had an open route to Syria and moved against the other Muslim powers in the region . </P> <P> His army advanced towards Ayyubid - ruled Syria, capturing small local states en route . The sultan Al - Nasir Yusuf of the Ayyubids refused to show himself before Hulagu; however, he had accepted Mongol supremacy two decades earlier . When Hulagu headed further west, the Armenians from Cilicia, the Seljuks from Rum and the Christian realms of Antioch and Tripoli submitted to Mongol authority, joining the them in their assault against the Muslims . While some cities surrendered without resisting, others such as Mayafarriqin fought back; their populations were massacred and the cities were sacked . </P> <P> Meanwhile, in the northwestern portion of the empire, Batu's successor and younger brother Berke sent punitive expeditions to Ukraine, Belarus, Lithuania and Poland . Dissension began brewing between the northwestern and southwestern sections of the Mongol Empire as Batu suspected that Hulagu's invasion of Western Asia would result in the elimination of Batu's own dominance there . </P> <P> In the southern part of the empire, Möngke Khan himself led his army to complete the conquest of China . Military operations were generally successful, but prolonged, so the forces did not withdraw to the north as was customary when the weather turned hot . Disease ravaged the Mongol forces with bloody epidemics, and Möngke died there on 11 August 1259 . This event began a new chapter in the history of the Mongols, as again a decision needed to be made on a new great khan . Mongol armies across the empire withdrew from their campaigns to convene a new kurultai . </P>

In the mongol empire a khan was a