While the seventh king of Goryeo, King Mokjong(穆宗; r. Oct. 997~ Feb. 1009) was the son of the fifth king King Gyeongjong(景宗; r. May 97 5~July 981), he was raised by his uncle on his mother’s side, King Seongjong(成宗; r. July 981~Oct. 997) and ascended the throne at the age of 18 after the death of King Seongjong. However, during the period of his reign, his mother, Queen Cheonchu(or Cheonchu-taehu 千秋太后), exercised great influence over state affairs and her lover Kim Chi-Yang(金致陽) rapidly rose as a political power. In addition, while King Mokjong had no child, in the sixth year of his reign, a son was born between Cheonchu-taehu and Kim Chi-Yang. As Cheonchu-taehu wanted her son to become heir to the throne of King Mokjong, political conflicts erupted over the succession of the throne.
This problem politically surfaced when a fire in the oil storage in Daebu(大府, Bureau of the Palace Bursary), a managemental organization of royal documents and fortunes, spread and burned up the House of Cheonchu-taehu, Cheonchu-jeon(千秋殿) in January 16, 1009 (12th year of the reign of King Mokjong). Following this event, King Mokjong became ill and did not administer the affairs of state while closing the palace and shutting himself up inside it. This resulted in an extreme political chaos. King Mokjong called in Gang Jo(康兆) who was in Western Capital Seogyeong(西京; modern Pyeongyang) and had him protect his security. On the other hand, He recalled in prince priest Daeryangwon(later Hyeonjong) to capital Gaegyeong(開京; modern Gaeseong) and sought to resolve the chaos by designating him as the heir to the throne. However, by misunderstanding that King Mokjong was murdered by the faction of Kim Chi-Yang, Gang Jo staged a coup for the apparent cause of removing the fraction of Kim Chi-Yang. As a result, Kim Chi-Yang was killed, and then King Mokjong was dethroned in February 2 and King Hyeonjong(顯宗; r. Feb. 1009~May 1031) was enthroned in February 3. In doing so, this event was concluded in 18 days. And a few days later, King Mokjong was killed by Gang Jo.
Gang Jo, who had seized power by staging a coup with the military power of Seogyeong, integrated Jungchuwon(中樞院, Privy Council), Seonhwiwon(宣徽院, Institute of Palace Miscellaneousness), and Eundae(銀 臺, Office of Transmission), which are the administrative offices of the king’s aide, into Jungdaeseong(中臺省, Palace Secretariat). He appointed himself as its minister since then. These offices had it common that they were the offices in charge of intimately serving the king. Jungchuwon was the representative office to serve the king and in charge of receiving and passing the king’s orders to other offices. Seonhwiwon is presumed to have supervised the palace in which the king resided, including the handling of various miscellaneous events such as ceremonies and rituals within the palace. Finally, Eundae was in charge of the administration of central and local documentation, in other words, the process of delivering the king’s orders. In fact, these offices hint at the purpose for which Gang Jo installed Jungdaeseong. Given that Gang Jo enthroned King Hyeonjong and killed King Mokjong by mounting a coup with 5,000 soldiers in Seogyeong, he was already in control of military power from the early reign of King Hyeonjong. Based on this, he could seize practical political power. Despite this fact, because Gang Jo did not hold an important post in terms of the governing structure, he could potentially be isolated from the process of political decision making. As he had seized power through the emergency means of coupe, he must have placed great importance on the prevention of another potential coupe. Eventually, Gang Jo intended to eliminate such a likelihood for another coupe by gaining control over the courses of protecting the king’s security, receiving and forwarding the king’s orders, and delivering the king’s orders through documentation through a single office called Jungdaeseong. In addition, its installation may have had the meaning of checking and keeping an eye on the king. This may have been the key cause for the formation of Jungdaeseong. For this reason, King Hyeonjong, who had fled down to Naju due to the war with Khitan Liao, abolished the office in February 1011 during his return to Gaegyeong as soon as he heard the news that Gang Jo was captured and killed by Gang Jo in November 1010 and Khitan Liao retreated in January 1011.