Mongol Invasions of Korea - The Initial Campaigns

The Initial Campaigns

Gojong of Goryeo (reigned 1213–1259) was the 23rd king of the Goryeo dynasty. In 1225, the Mongol Empire demanded tribute goods from Goryeo and the Mongol envoy Chu-ku-yu was killed. His death was used by the Mongols as an excuse to invade Goryeo.

In 1231, Ögedei Khan ordered the invasion of Korea. The experienced Mongol army was placed under the command of General Sartai (not to be confused with Sartaq, a later Mongol khan). The Mongol army crossed the Yalu river and quickly secured the surrender of the border town of Uiju. Choe U mobilized as many soldiers as possible into an army consisting largely of infantry, where it fought the Mongols at both Anju and Kusong. The Mongols took Anju; however, they were forced to retreat after the Siege of Kusong. Frustrated by siege warfare, Sartai instead used his armies' superior mobility to bypass the Goryeo army and succeeded in taking the capital at Gaesong. Elements of the Mongol army reached as far as Chungju in the central Korean peninsula; however, their advance was halted by a slave army led by Ji Gwang-su where his army fought to the death. Realizing that with the fall of the capital Goryeo was unable to resist the Mongol invaders, Goryeo sued for peace. However, Mongols demanded 10,000 otter skins, 20,000 horses, 10,000 bolts of silk, clothing for 1,000,000 soldiers and a large number of children and craftsmen who would become slaves and servants of the Mongol empire. General Sartai began withdrawing his main force to the north in the spring of 1232, leaving seventy-two Mongol administrative officials stationed in various cities in northwestern Koryo to ensure that Koryo kept his peace terms.

In 1232, Choe U, against the pleas of both King Kojong and many of his senior civil officials, ordered the Imperial Court and most of Gaesong's population to be moved from Songdo to Ganghwa Island in the Bay of Gyeonggi, and started the construction of significant defenses to prepare for the Mongol threat. Choe U exploited the Mongols' primary weakness, fear of the sea. The government commandeered every available ship and barge to transport supplies and soldiers to Ganghwa Island. The evacuation was so sudden that King Kojong himself had to sleep in a local inn on the island. The government further ordered the common people to flee the countryside and take shelter in major cities and mountain citadels or nearby offshore islands. Ganghwa Island itself was a strong defensive fortress. Smaller fortresses were built on the mainland side of the island and a double wall was also built across the ridges of Mt. Munsusan.

The Mongols protested the move and immediately launched a second attack. The Mongol army was led by a traitor from Pyongyang called Hong Bok-won and the Mongols occupied much of northern Korea. Although they reached parts of the southern peninsula as well, the Mongols failed to capture Ganghwa Island, which was only a few miles from shore, and were repelled in Gwangju. The Mongol general there, Sartai (撒禮塔), was killed by the monk Kim Yun-hu (김윤후) amidst strong civilian resistance at the Battle of Cheoin near Yongin, forcing the Mongols to withdraw again. This was the first of only two instances in which a Mongol commander was ever killed in battle (the other being the Battle of Ain Jalut in 1260, where Kitbuqa was killed).