We see that the Emperor had virtually decided in favor of Sil-la as against Păk-je and Ko-gu-ryŭ. The long expected event had at last occurred. Tacitly but really China had cast her vote for Sil-la and the future of the peninsula was decided for so long as the Tang dynasty should last. That the decision was a wise one a moment’s consideration will show. Ko-gu-ryŭ never could be depended upon for six months in advance and must be constantly watched; Păk-je, being really a mixture of the northern and southern elements, had neither the power of the one nor the peaceful disposition of the other but was as unstable as a cloud. Sil-la on the other hand was purely southern, excepting for a strain of Chinese blood brought in by the refugees from the Tsin dynasty. Her temperament was even, her instincts peaceful, her tendencies toward improvement and reform. She was by all means the best ally China could have in the peninsula. And so the die was cast and henceforth the main drift of Chinese sympathy is to be Sil-la-ward.
The year 644 was a fateful one for Korea. The Emperor sent an envoy to Ko-gu-ryŭ and Păk-je commanding them to cease their depredations on Sil-la. Thus was the Chinese policy announced. Păk-je hastened to comply but Hap So-mun of Ko-gu-ryŭ replied that this was an ancient feud with Sil-la and could not be set aside until Ko-gu-ryŭ recovered 500 _li_ of territory that she had been despoiled of. The Emperor in anger sent another envoy with the same demand, but Hap So-mun threw him into prison and defied China. When he heard however that the Emperor had determined upon an invasion of Ko-gu-ryŭ he changed his mind and sent a present of gold to the Chinese court. But he was too late. The gold was returned and the envoy thrown into prison.
There were many at the Chinese court who could remember the horrors of that retreat from P’yŭng-yang when China left 300,000 dead upon the hills of Ko-gu-ryŭ, and the Emperor was advised to move cautiously. He however felt that unless Ko-go-ryŭ was chastised she might develop an ambition towards imperialism and the throne of China itself might be endangered. He therefore began to collect provisions on the northern border, storing them at Tă-in Fortress. He called into his counsels the old general, Chöng Wŭn-do, who had been an eye-witness of the disasters of the late war with Ko-gu-ryŭ. This man gave healthful advice, saying that the subjugation of Ko-gu-ryŭ would be no easy task; first, because the way was so long; second, because of the difficulty of provisioning the army; third, because of the stubborn resistance of Ko-gu-ryŭ’s soldiers. He gave the enemy their due and did not minimize the difficulties of the situation.