Genghis Khan had been having a serious internal family problem during the later campaigns. Although he had promoted on a merit basis for years, and although he railed against aristocratic inheritance, in truth of course he wanted his sons to be Khans after he died. One of his sons would be the Great Khan with authority over the others. He had always favored Jochi, the oldest, for this role, but the second son Chagatai believed that Jochi was the son of a Merkit warrior and should not inherit.
(credit to Jack Weatherford, Genghis Khan and the Making of the Modern World)
In a family conference, the Khan tried to address the succession question, but Jochi and Chagatai got into a vicious fistfight. The Khan pleaded with them all to accept Jochi as a brother, to honor their mother, who had after all been kidnapped during a time when his rule had not yet imposed peace. The best compromise they could reach was that neither Jochi nor Chagatai would become Great Khan, but instead the third brother Ogedei would inherit this title. Jochi was furious, but the agreement was made. With that understanding, Genghis Khan assigned them zones to rule, separating their future kingdoms as far as possible, and leaving the central homeland to his youngest son Tolui by Mongol tradition.
Here’s another point where Mongol culture is so different from the West: inheritance by the youngest. It makes perfect sense if you think of steppe life where survival is better if people spread out to find new resources. When the oldest son is grown, he will marry and have a herd of his own, gradually spreading farther away to find other hunting grounds. The original family will stay together as the other sons also spread out. When the parents get old, the youngest is still at home. Mongols called the youngest the Ochigen, the Prince of the Hearth. He would have the responsibility of his parents’ care, and would get their possessions or territory.
Jochi was given the territories farthest away: the west, where as yet little land had been won. It was clear that there was much room for relatively easy conquest, and those new lands would belong to Jochi’s branch. Chagatai got the just-conquered regions that are now Kazakhstan, Uzbekistan and Afghanistan. Ögedei inherited the Chinese regions in the east, as well as the nod for Great Khan. He was the most sociable of the sons and the Khan hoped he could keep the family branches unified. Tolui, the Ochigen, inherited the Mongolian homeland where his mother still lived.
Tolui’s mother Börte was now very old; she had stopped traveling with Temujin long ago, leaving that hassle to younger wives. The Great Khan had a string of marriage alliances, but only managed four wives at a time. When he had to take a new one, he passed an old one off to a brother or general, except for Börte who counted as his official queen. Now about 65, the Great Khan realized he had one more expedition to make, putting down a rebellion among the Tanguts of western China. In 1226, he saddled up again, choosing a younger Tatar wife named Yesui to accompany him.
In the Gobi Desert, he hunted wild horses and was badly injured. He probably developed an internal infection but he was determined to push through it. The campaign against the Tanguts went forward, and he succeeded in punishing their rebel king. But by the end of the summer, he died. Yesui wrapped him in a felt coffin packed with sandalwood chips, and his army carried his body home.
Here’s where it gets strange. Temujin’s ancestral burial tradition had been open-air, leaving the body for sacred vultures, but legends say variously that he chose to be buried with six cats, that he was buried underground with treasures from around his empire, or that he was buried on top of his sacred mountain. A persistent legend says that in order to hide the place, his army trampled the ground with a thousand horses, covering their trail and a wide berth around it.