The 100-year history of the Military regime weakened Goryeo's royal authority. Choi's political power trampled on the king's authority and maintained the authority of the royal court to avoid the attack of his political opponents and to surpass the power of the king. Under the long war and oppression of the Mongols, the crown prince (King Won-jong) entered the Mongol Court. After the death of King Go-jong, in 1260 Won-jong took the throne with full support from Kubilai. However, he was demoted by Im-yeon in 1269 in an unstable symbiotic relationship with the Military regime, and was restored by Mongolian authority. However, This accident leads that Crown Prince (King Chungnyeol) asked Kubilai to marry the princess and thus become his son-in-law. The close relationship between Mongolia and Goryeo King actually began at this time. Becoming a son-in-law of the emperor means “the one who deserves to be king among the Dragon’s Descendants.” As a result, the political history of the late Goryeo Dynasty developed into a political dispute between the emperor's sons-in-law. The reinstate(重祚) is the result of political wrangling among the ‘King of Emperor’s sons-in-law’. However, in terms of relations with Mongolia, marriage was the most important but not the only one. King Chungseon, who is a mixed-race prince, has a special “blood relationship” with the Mongolian royal family as the grandson of Kubilai in addition to his marriage. Having lost his throne due to his feud with the princess, King Chungseon formed a strong “background” (根脚) by helping Emperors Mujong (武宗) and Renjong (仁宗), thus overcoming the instability of the marriage and regaining the authority of Goryeo King. Having gained great power as king, King Chungseon stayed on the Dadu (大都) for a long time and practiced Remote control rule (遙領統治). But under constant pressure to return to Goryeo, King Chungseon nominated the king (Chungsuk) and the Crown prince (Wang Go) simultaneously in 1313. Furthermore, they married the princess in the same year in 1316. As a result, King Chungseon created two sons-in-law of the emperor, who deserves to be king among the Dragon’s Descendants at the same time. Shim Wang (瀋王) Wang Go (王暠) was favored by King Chungseon and became a son-in-law of the Emperor through his marriage to the princess, so he was entitled to become a king among the Dragon’s Descendants. Later, however, Wang Go lost his position as a Crown prince. To regain his right to succeed to the throne, he was forced to face King Chungsook. The princess of the Wang Go was much higher in stature than the princess of King Chungsuk. By participating in the imperial struggle within the empire that broke out after the death of Emperor (泰定帝) in 1328, Wang Go sought to form a another strong “background” like King Chungseon. But it eventually failed. Relationship which had been based on marriage, have collapsed as the growth of Empress Ki(奇)’s power, which threaten the Goryeo Dynasty, and the “breedy prince” of her child, sought the next throne. At this time, Goryeo King’s authority expanded to the royal authority in response to the challenge of Ki’s power, who threatened the Yuan empire. Now, among the Dragon’s Descendants there is no need to be a son-in-law of the emperor in order to succeed to the Goryeo’s throne. Instead, with the emphasis on legitimate and lineal relatives between the royal family, Wang Go was already regarded as the ‘collateral line’ who sought the throne at that time. King Gongmin lifted his pigtail and exotic costume in 1352, the following year after his ascension to the throne. In short, until King Chungnyeol wore pigtail and King Gongmin took it off, the Mongolian emperor was a political supporter of the Goryeo kingship. The marriage was the most important foundation in the relationship between Goryeo kings and Mongol. The breakdown of the marriage relationship has since brought about a major change in the relationship between the two Dynasties.