Tora Jane had planted herself in the favor of Karakoram aristocrats through lots of favors and heavy corruption. Those in the empire capital supported the secession of her son Guyuk however for him to become Great Khan all Khans must attend the Kurultai. Batu of the golden horde refused to attend claiming illness. This started the early steps of the fall of the mongols
The youngest of Tolo sones Eric Bakker would have himself elected as great khan. His siblings didnt really agree leading to more divisions with the family. Kublai would call a Kurultai on his own territory in northern China and elected great khan. There were two great khans at the same time resulting in futher conflict.