At the instigation of Hap So-mun, the king of Ko-gu-ryŭ sent his son to China, confessed his faults and begged for mercy, but the Emperor’s face was flint. The next year the message was again sent, but Ko-gu-ryŭ’s day of grace was over. China’s answer was an army of 30,000 men and a mighty fleet of ships. The fortress of Pak-chak in Liao-tung was besieged but it was so fortified by nature as to be almost impregnable. The Emperor therefore said “Return to China and next year we will send 300,000 men instead of 30,000.” He then ordered the building of a war vessel 100 feet in length. He also had large store of provisions placed on O-ho Island to be used by the invading army.
Meanwhile Sil-la had become emboldened by the professed preference of China for her and she arose and smote Păk-je, taking twenty-one of her forts, killing 30,000 of her soldiers and carrying away 9,000 prisoners. She followed this up by making a strong appeal to China for help, saying that unless China should come to her aid she would be unable to continue her embassies to the Chinese court. The Emperor thereupon ordered Gen. So Chöng-bang to take 200,000 troops and go to the aid of Sil-la. He evidently was intending to try a new way of attacking Ko-gu-ryŭ. As the Sil-la messenger was hastening homeward with this happy news emissaries of Ko-gu-ryŭ dogged his footsteps and sought his life. Once he was so hard pressed that he escaped only by a clever and costly ruse. One of his suite dressed in his official garments and personated him and thus drew the assassins off the scent and allowed himself to be killed, the real envoy making good his escape. It was now for the first time that Sil-la adopted the Chinese costume, having first obtained leave from the Emperor. It is said that it resembled closely the costume used in Korea today.
Unfortunately for Sil-la the Emperor died in 649 and Ko-gu-ryŭ began to breathe freely again. It also emboldened Păk-je and she invaded Sil-la with a considerable army and seized seven forts. Sil-la retaliated by seizing 10,000 houses belonging to Păk-je subjects and killing the leading Păk-je general, Eum-sang. Sil-la lost not a moment in gaining the good will of the new Emperor. Envoys with presents were sent frequently. She adopted the Chinese calendar and other customs from the suzerain state and so curried favor with the powerful. The Păk-je envoy was received coldly by the Emperor and was told to go and give back to Sil-la the land that had been taken and to cease the hostilities. This Păk-je politely declined to do. Each emperor of China seems to have declined the legacy of quarrels handed down by his predecessor. So bye-gones were bye-gones and Ko-gu-ryŭ was accepted again on her good behavior.