Mongke’s brother Kublai is thirty-eight in 1253 when, ordered to attack Yunnan to outflank the Song, he leads one hundred thousand soldiers through eastern Tibet to Yunnan.

It is claimed that despite their military prowess and superior numbers, the Mongols could not breach the defenses of the Erhai valley, which was so suited to defense that even just a few defenders could hold out for years.

It is said that the Mongols had found a traitor who led them over the Cangshan mountains along a secret path, and only in this way were they able to penetrate and overrun the Bai defenders.

Thus ends five centuries of Bai independence.

Turning back a flank of the Song army, Kublai marches his troops through Laos to attack the Song southern flank.