When the Mongol conquest of the Song dynasty was completed in 1279. Kublai became the first non-native emperor to conquer all of China.
When Byamba returns to Kaidu's camp his horse carries several severed heads; the heads belonged to the eight Kaidu soldiers who accompanied Byamba to the capital. The heads were presumably chopped off by Kublai himself as depicted in the strange scene where a half-naked Kublai slashes something with his sword.