The Korea-Khitan War was a 26-year-long war between the Khitan Empire, a great power of the time, and Goryeo, an emerging state. As King Mokjong left no heirs from being preoccupied, King Hyeonjong, the last grandson of Taejo of Goryeo, became 1st in line for succession. King Hyeonjong, who had been away from politics and living as a monk, ascended to the throne at 19 years of age due to a rebellion by Kang Cho. The young king faced an invasion by a Khitan army of 400,000 men. The king's 70-year-old subject, Kang Kam Chan, scolded the petrified king, but King Hyeonjong took a liking to Kam Chan and entrusted him with the defense against the Khitan invasion. King Hyeonjong unified Goryeo with his tolerance and leadership, and along with Kam Chan, his teacher in politics, and many other subjects, he managed to withstand 6 Khitan invasions, eventually annihilating the Khitan army at the Battle of Kwiju led by Kam Chan and seizing victory by utilizing Goryeo's own strength.