Back when Mongolia conquered the world, there were three people who were most capable of competing for the throne of Khan after his death, namely Kublai Khan, Ali Bug and Xu Liewu. Unlike the Han nationality, Mongols choose their heirs. The youngest son inherits the family business, so according to the custom, Xu Liewu is the one who should inherit the throne most.
However, after a long period of development, the selection method of Mongolian Khan is no longer to see who is older and who is younger, but to see who has the greatest meritorious military service and whose fist is bigger. This is actually related to Mongolian customs. Mongols worship force very much. If you let a weak soft egg sweat, it will definitely cause many people's dissatisfaction. Therefore, although the younger son inherited the family business, it was gradually abandoned in the process of Mongolia's rise.
Brother Ali didn't fight any battles, and the troops in his hand were all picked by Kublai Khan and Xu Liewu, so naturally he couldn't beat Kublai Khan. In addition, Alibaba has no prestige and has never made any meritorious military service. Of course, Xu Liewu will not support those who have little chance of winning.
In addition, in the process of seizing power with Ali Buge, Kublai Khan personally made a promise to Xu Liewu, saying that as long as he wanted the Central Plains, he would not get his hands on West Asia shot down by Xu Liewu. Under this condition, Xu Liewu will naturally choose to support Kublai Khan instead of Ali Buge.