The Song Dynasty – the Mongol Empire's most powerful rival – saw Genghis Khan's grandson die during conquest, a direct cause of the Mongol Empire's fragmentation.

In 1259, Genghis Khan's grandson, Möngke Khan, died in the war to conquer Song Dynasty China, causing a rift in the Mongol Empire. In 1260, Kublai and Ariq Böke each declared themselves Khan, igniting a civil war within the Mongol Empire. In 1264, Kublai Khan won the war and established the Yuan D