Kublai's invasion of Japan in 1274 involved 8,000 Korean troops. The second invasion of 1281 was, in fact, a combined operation between Mongolia and Goryeo. In 1287, Nayan, descendant of Genghis Khan's younger brother, and Qaidu, descendant of Augusta, rebelled against the Yuan Dynasty in 1287. Kublai, who was old, had no power to ride a horse. Still, he decided to lead his army himself, and went to Lake Buir. There he defeated Nayan's army and moved to the Hangai Mountains to attack Qaidu. And in 1292, the combined forces of Mongolia and Korea completely suppressed the rebellion.
