A series of campaigns were conducted between 1231 and 1270 by the Mongol Empire against the Goryeo dynasty of Korea. There were seven major campaigns at tremendous cost to civilian lives, the last campaign made Goryeo a vassal state of the Yuan dynasty for approximately 80 years. The Yuan dynasty would exact wealth and tributes from the Goryeo kings. Despite submission to the Yuan dynasty, internal struggles among Goryeo royalty and rebellions against Yuan rule would continue, the most famous being the Sambyeolcho Rebellion. A greater amount of "stubborn resistance" was put up by Korea and Song Dynasty towards the Mongol invasions than many others in Eurasia who were swiftly crushed by the Mongols at a lightning pace. The initial campaigns Fleeing from the Mongols, in 1216 the Khitans invaded Goryeo and defeated the Korean armies multiple times, even reaching the gates of the capital and raiding deep into the south, but were defeated by Korean General Kim Chwi-ryeo who pushed them back north to Pyongan, where the remaining Khitans were finished off by allied Mongol-Goryeo forces in 1219. These Khitans are possibly the origin of the Baekjeong. Gojong of Goryeo (reigned 1213–1259) was the 23rd king of the Goryeo dynasty of Korea. 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 a pretext to invade Goryeo. First Mongol invasion of Korea (August 1231 – January 1232) In 1231, Ögedei Khan ordered the invasion of Korea. The experienced Mongol army was placed under the command of General Saritai (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. The Mongols were joined by Hong Bok-won, a traitor Goryeo general. Choe Woo mobilized as many soldiers as possible into an army consisting largely of infantry, where it fought the Mongols at both Anju and Kuju (modern-day Kusong). The Mongols took Anju; however, they were forced to retreat after the Siege of Kuju. Frustrated by siege warfare, Saritai 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