quality:corruption, linguistic:paraphrasing, structural:expansion
Post-Ögedei power struggles (1241–1251)

Following the Great Khan Ögedei's death in 1241, and before the next kurultai, Ögedei's widow Töregene took over the empire. She persecuted her husband's Khitan and Muslim officials and gave high positions to her own allies. She built palaces, cathedrals, and social structures on an imperial scale, supporting religion and education. She was able to win over most Mongol aristocrats to support Ögedei's son Güyük. But Batu, ruler of the Golden Horde, refused to come to the kurultai, claiming that he was ill and that the climate was too harsh for him. The resulting stalemate lasted more than four years and further destabilized the unity of the empire.

When Genghis Khan's youngest brother Temüge threatened to seize the throne, Güyük came to Karakorum to try to secure his position. Batu eventually agreed to send his brothers and generals to the kurultai convened by Töregene in 1246. Güyük by this time was ill and alcoholic, but his campaigns in Manchuria and Europe gave him the kind of stature necessary for a great khan. He was duly elected at a ceremony attended by Mongols and foreign dignitaries from both within and without the empire — leaders of vassal nations, representatives from Rome, and other entities who came to the kurultai to show their respects and conduct diplomacy.

Güyük took steps to reduce corruption, announcing that he would continue the policies of his father Ögedei, not those of Töregene. He punished Töregene's supporters, except for governor Arghun the Elder. He also replaced young Qara Hülëgü, the khan of the Chagatai Khanate, with his favorite cousin Yesü Möngke, to assert his newly conferred powers. He restored his father's officials to their former positions and was surrounded by Uyghur, Naiman and Central Asian officials, favoring Han Chinese commanders who had helped his father conquer Northern China. He continued military operations in Korea, advanced into Song China in the south, and into Iraq in the west, and ordered an empire-wide census. Güyük also divided the Sultanate of Rum between Izz-ad-Din Kaykawus and Rukn ad-Din Kilij Arslan, though Kaykawus disagreed with this decision.

Not all parts of the empire respected Güyük's election. The Hashshashins, former Mongol allies whose Grand Master Hasan Jalalud-Din had offered his submission to Genghis Khan in 1221, angered Güyük by refusing to submit. Instead he murdered the Mongol generals in Persia. Güyük appointed his best friend's father Eljigidei as chief commander of the troops in Persia and gave them the task of both reducing the strongholds of the Nizari Ismailis and conquering the Abbasids at the center of the Islamic world, Iran and Iraq.