The key to this great struggle, which resulted in the advancement of Sil-la to the control of the whole peninsula, lay not so much in the relative military strength of the three rival kingdoms as in the skill which each developed in diplomacy. Each was trying to gain the active support of China, knowing very well that if China should once become thoroughly interested in favor of any one of the three powers the other two would be doomed. We will remember that Ko-gu-ryŭ had cultivated friendly relations with the Sung dynasty while Păk-je had made herself agreeable to the Wei dynasty. In this Păk-je chose the wiser part for the Wei power was nearer and more powerful. In 466 Ko-gu-ryŭ lost a splendid opportunity to establish herself in the good graces of the Wei Emperor, and so insure her preeminence in the peninsula. The Emperor Hsien-wen made friendly advances and requested the daughter of the king of Ko-gu-ryŭ for his wife. With a short-sightedness that is quite inexplicable this request was put off by the lame excuse that his daughter was dead. This being easily proved a falsehood, Ko-gu-ryŭ fell from the good graces of the very power whose friendship she should have cultivated. The year 467 witnessed an important innovation in Korea. Sil-la took the lead in the construction of war vessels. The one made at that time was doubtless intended for use against the Japanese corsairs. That Sil-la had been gaining along military lines is shown by her successful repulse of a Ko-gu-ryŭ invasion in this year, in which the wild people of some of the Mal-gal tribes assisted Ko-gu-ryŭ. After the latter had been driven back, Sil-la built a fortress at Po-eun on her northern border to guard against a repetition of this invasion. Ko-gu-ryŭ and Păk-je were now exerting themselves to the utmost to make capital out of their Chinese alliances. Ko-gu-ryŭ sent rich presents and richer words to the Sung capital and so won the confidence of that power. Păk-je, on the other hand, sent word to the Wei Emperor that Ko-gu-ryŭ was coquetting with the Sung court and with the wild Mal-gal tribes, insinuating that this was all detrimental to the interests of Păk-je’s patron.