After signing a brotherhood pact with Mongol in 1219, Goryeo also established certain diplomatic relations with Dongjin(東眞). The Dongjin envoy came to Goryeo from 1219 to 1222 as an assistant to the Mongol envoy toward Galaro(曷懶路). They were responsible for guiding the Mongol envoy, escorting and transporting Mongol envoys, and distributing Mongol envoys and crafts.
Dongjin fell to Mongol in January 1224, and offered Hwachin to the Goryeo side on the condition that Gakjang(榷場) be installed. Dongjin’s request for the installation of Gakjang was intended to solvetheirfoodshortagesanddailynecessities.Goryeodidnotaccept Dongjin’s request for the establishment of Gakjang, mainly because ofconcernsthatGoryeo’sfriendlyrelationswithDongjinandbetraying Mongol would lead to Mongol invasion in the future.
After Goryeo rejected Dongjin’s offer to installation of Gakjang, the war began between Goryeo and Dongjin from 1225. Later, in September 1227, when Dongjin-gun invaded Jeongju(定州) and Jangju(長州), the Choi Woo(崔瑀)’s political power formed three Goryeo troops to fight, but was defeated in the Battle of Uiju(宜州). However, Kim Yi-saeng(金利生), Nangjang(郎將) of Bukgye, fought the Dongjin Army at Hwaju Castle(和州城) and cut 1,100 enemies. This put an end to the war with Dongjin.
DongjinsuddenlyofferedHwachintotheGoryeoinFebruary1229.
This was because Dongjin had a great sense of crisis as Mongol, which began to attack Liaodong(遼東). King Gojong(高宗) dispatched No Yeon(盧演), Sikmoknoksa(式目錄事) to Dongjin to find out the conditions of Dongjin’s Hwachin, but No Yeon was unable to carry out his mission. As a result, the military ruler, Choi Woo sent Jin Yong-gap(陳龍甲), a former Geoje-hyeon-ryeong(巨濟縣令), to form a friendly relationship with Dongjin, and it is estimated that Jin Yong-gap had reached a state of coordinating the conditions of reconciliation with Dongjin. At a time when Jin Yong-gap was persuading Dongjin, Choi Jong-jae(崔宗梓), Byeongmasa of Donggye (東界兵馬使) sent Yejak(銳爵) to Dongjin to promote Dongjin and HwachinwithoutreportingittotheGoryeoDynasty.However,Yejak was mistaken for a spy and executed in Dongjin. Despite Yejak execution case, it is believed that the Choi Woo’s political power has maintained an attitude to pursue diplomatic negotiations with Dongjin, such as the exchange of diplomatic documents.