Although Goryeo made peace with the Mongols, it was subject to strong Mongol dominance for over a century. The Mongols changed the named of its state to Yuan. Unlike its other conquered regions which it ruled harshly, the Yuan allowed the unique systems and customs of Goryeo to be maintained and exerted influence indirectly through the king of Goryeo. Yuan had to acknowledge that Goryeo was a strong nation with a highly advanced level of culture.
At the demand of the Yuan, however, Goryeo was forced to mobilize for an expedition to Japan. It was also forced to provide war supplies including ships, food, weapons, and military forces. The Yuan also demanded Goryeo to make various tributary payments such as gold, silver, ginseng and falcons. They even demanded women. Under these excessive demands, Goryeo went through the most difficult period of its time. Yuan seized Jeju Island and turned it into a meadow raising horses (Tamna Commandery). Some of the territory in the northern area was also taken by Yuan (Ssangseong Commandery, Dongnyeong Commandery). The crown prince of Goryeo was forced to wed a Yuan princess and the king’s names used the prefix character ‘loyal’(chung) as a means of characterizing thier loyalty to the Yuan. All the terms relating to the king and his actions were downgraded, and various systems of Goryeo were changed. Those who rose to power by supporting the Yuan took hold of much land, turned the peasants into slaves and, engaged in many oppressive acts. The lives of the peasantry became more difficult and the financial state of the country became further pressed.
Through their cultural exchanges the Mongol customs gained great popularity among the ruling class of Goryeo, some of which remain to this day. Jokduri, a type of headpiece worn by brides in their weddings, lipsticks, and silver knives, all originated from the Mongols. On the other hand, the customs of Goryeo such as dumplings and rice cakes were passed to the Mongol society and became greatly popular.