As the end of the sixth century Goguryeo began to attack on Silla. King Youngryu who came to throne in A.D. 618 also attacked on Silla, however after A.D. 638 fighting with Silla came to a standstill. Naturally there were groups who had dissatisfaction with such the situation, they were Yeongaesomoon, etc. After the death of his father, Yeongaesomoon had a difficulty with the just succession of status. Therefore he mounted a coup solidarizing with Daeyang Group, and enthroned King Bojang who had similar recognition in Silla. But Yeongaesomoon regime was challenged in and out. There were resist groups as Ansisung castellan inside, and aggravation in relation Tang of attack on Silla. Yeongaesomoon attacked Silla immediately after the coup, and refused the Silla`s asking for a dispatch of troops after the battle of Daeyasung. Meanwhile Taizong of Tang demanded aborting the attack on Silla, and put pressure on Goguryeo. Yeongaesomoon insisted the attak on Silla continuously, then he suffered the Tang`s expedition with the lack of preparation. Therefore his hard-line policy on Silla was also delayed. Developing similar situation of early seventh century, Goguryeo`s fate was affected.