Korai soon came into collision with the Kitans in the following manner. The royal line of united Corea traced their descent directly from the ancient kings of Kokorai, and therefore claimed relationship with the princes of Puhai. On the strength of this claim, the Koraian king asserted his right to the whole of Liao Tung, which had been formerly held by Puhai. The Kitans, having matters of greater importance to attend to at the time, allowed its temporary occupation by Korai troops. Nevertheless the king thought it best to send homage to the Kitan emperor, in order to get a clear title to the territory. In 1012 he despatched an embassy acknowledging the Kitan supremacy. This verbal message did not satisfy the strong conqueror, who demanded that the Koraian king should come in person and make obeisance. The latter refused. A feud at once broke out between them, which led to a war, in which Korai was worsted and stripped of all her territory west of the Yalu River. Palladius has pointed out the interesting fact that a little village about twenty miles north of Tie-ling, and seventy miles north of Mukden, called Gauli-chan (Korai village) still witnesses by its name to its former history, and to the possession by Corea of territory west of the Yalu. The Kitans, not satisfied with recovering Liao Tung, crossed the river and invaded Korai, in 1015. By this time a new nation, under the name of Nüjun or Ninchi, had formed around Lake Hanka, in part of the territory of extinct Puhai. With their new frontagers the Koraians made an alliance “as solid as iron and stone,” and with their aid drove back the Kitan invaders. Henceforth the boundaries of Corea remained stationary, and have never extended beyond the limits with which the western world is familiar. An era of peace and prosperity set in, and a thriving trade sprang up between the Nüjun and Korai. The two nations, cemented in friendship through a common fear of the Kitans, grew apace in numbers and prosperity. The Kitans were known to Chinese authors as early as the fifth century, seven nomad tribes being at that time confederate under their banners. At the beginning of the tenth century, these wanderers had been transformed into hordes of disciplined cavalry. Their wealth and intelligence having increased by conquest, they formed a great empire in 925, which extended from the Altai Mountains to the Pacific Ocean, and from within the Great Wall to the Yablonoi Mountains, having Peking for one of its capitals. It flourished until the twelfth century (A.D. 1125), when it gave way to the Kin empire, which held Mongolia and still more territory than the Kitans possessed within what is now China proper.