Before he died, Genghis Khan appointed his second son Ögödei (died 1241) as his successor, and ruler of the Siberian portion of the empire. His eldest son Jochi had died in 1226 - his share, the lands of the West (as " reconnoitred" by Jebe and Sübedei), passed to his son Batu. Chagatai (died 1242) received eastern Turkestan and western China. The youngest, Tolui (died 1232) became ruler of the ancestral Mongolian lands.
Batu son of Jochi, by 1241, had extended the empire further northwards and westwards into Russia and eastern Europe as far as the Adriatic coast. As leaders of the "Golden Horde" his family (Batu died in 1255) was soon to find itself in competition with another branch of the family. Tolui, youngest son of Genghis, had three sons. In 1251, after a "bloody and contentious election", the eldest of them, Möngke became Great Khan, and sent his brother Qubilai east to complete the conquest of China, and Hülegü to complete the western conquests.
Hülegü - the Il-Khan
The Il-Khan Hülegü and his Christian wife Dokuz Kathun, from a 14th century MS
Elimination of the Ismailis
In 1253 , the Il-Khan was sent westward by the Great Khan Möngke with a vast army. But he was not just concerned with conquest - he showed that civil administration was of equal importance, by appointing Shams al-Din Juvaini (brother of the historian) as vizier. He held the post for over 20 years (1262 - 1284). Hülegü's military mission was to eliminate the two groups still holding out against the Mongols - the Ismailis and the Abbasid caliphate. In 1254, he reached the Oxus. His slow progress, and establishment of his capital in Azerbaijan at Marageh (later to move to Tabriz) encouraged not just trans-continental trade, but ambitious young men from Iran and Central Asia to attach themselves to his court. There he received pledges of submission from various regional rulers, including the Seljuq sultans of Rum (who had initially welcomed the stream of refugees from the destroyed cultural centres further east), and who had already accepted the status of vassals. It was not until spring 1256 that Hülegü finally reached his first objective: the Ismailis (Assassins) , who had successfully resisted the Seljuqs. 70 Ismaili mountain fortresses were demolished, with the cooperation of Rukn al-Din, the newly-appointed Grand Master of the Ismaili order - eventually even Alamut surrendered, and was demolished - though its library was saved. The castle at Gird-Kuh, though, held out for another 18 years. Rukn al-Din was showered with favours - until his usefulness expired. He and his entire family were then murdered - and a general massacre of Ismailis followed, on the direct orders of Möngke Khan according to one source.
The Ismaili Castle at Alamut, in the Alborz mountains near Qaswin, Iran
Destruction of the Abbasid Caliphate - capture of Baghdad
Having done this work to the benefit of Sunni Islam, Hülegü began his move towards Baghdad. The caliph had refused to help against the Ismailis, reluctant to risk troops he might need to defend his city. He began his attack, after demanding surrender, and being told to "go back where he came from". His astrologers prophesied doom if he dared to attack Baghdad, but Nasir al-Din Tusi, the famous astrologer/astronomer, a Shi'i, who had been rescued from Alamut on the direct order of Möngke (who hoped to use him to set up an astronomical school in Mongolia) was now in his entourage. He was able to reassure the Il-Khan that it was possible to remove a caliph without disaster befalling. The Mongol armies now moved in for the kill. The sack of Baghdad (February 1258) continued for seven days - its population being massacred as they exited the city to surrender. Only the houses of Christians were left standing. The caliph Musta'sim was executed by wrapping him in a carpet and then trampling him to death - to avoid shedding a caliph's blood. The Abbasid caliphate which had lasted just over 500 years was finally at an end.
Syria - temporary gains.
Hülegü next year set out to subdue Islamic lands further west - leaving Tabriz, he slaughtered the Kurds in the mountains of south-east Turkey, then went on into Mesopotamia: his objective being Aleppo, which fell after a six-day siege and ended in the usual massacre, which gave him control of Syria as far as Gaza (1260). He was poised to attack Egypt when he heard the news ( a year late!) of his brother Möngke's death, and started for home. But when his brother Qubilai was elevated to Great Khan (he was to become founder of the Yüan Dynasty in China), he came back to Tabriz - where he heard the news of a disastrous defeat in Syria. The Egyptian Mamluks had invaded and crushed the Mongols at Ain Jalut. Hülegü organised a counter-attack, which was also defeated, and the Mongols were forced to retreat to the Euphrates. Some European Christians had hoped that the Mongols - sympathetic to Christianity - would save the Crusaders and punish their Muslim enemies. Conversely the Mongols may have been hoping for help against the Ayyubids in Syria from Europe. Both sides were disappointed - although Öljeitü, Hülegü's great grandson was still hoping!
The Golden Horde
Berke, the current leader of the Golden Horde, inheritor of Jochi's and Batu's portion of Genghis' conquests north of the Caucasus, was apparently encroaching on territory which Hülegü believed was his, or rather Berke saw Hülegü as encroaching on his rights. He had also, as a Muslim convert, made an alliance with the Mamluk sultan, Baibars. Victories by Hülegü's forces were cancelled out by a major defeat (1263), after which many of his army were drowned when ice gave way as they retreated across the frozen river Terek. Hülegü retired to Tabriz, and plotted his revenge - but he died in 1265, leaving the leadership to his son Abaqa. His funeral was marked with human sacrifice - the last time this happened.
His wife died soon after - she was a Nestorian Christian, who presumably influenced her husband's leniency towards Christians. Mongol women, unlike their Islamic counterparts, had considerable power and status - their opinions counted. The Il-Khan and his successors paved the way for a national Iranian state - for the first time since the Sasanians Iran/Persia was a political entity, rather that a mere fact of geography - and direct diplomatic relations with the west were resumed. They ruled the greater part of the "Middle East" - though nominally still subjects of the Great Khan.