By the close of the ninth century the Nü-chêns had become subject to
the neighbouring Kitans, then under the rule of the vigorous Kitan
chieftain, Opaochi, who, in 907, proclaimed himself Emperor of an
independent kingdom with the dynastic title of Liao, said to mean
"iron," and who at once entered upon that long course of aggression
against China and encroachment upon her territory which was to result
in the practical division of the empire between the two powers, with the
Yellow River as boundary, K`ai-fêng as the Chinese capital, and Peking,
now for the first time raised to the status of a metropolis, as the
Kitan capital. Hitherto, the Kitans had recognised China as their
suzerain; they are first mentioned in Chinese history in A.D. 468, when
they sent ambassadors to court, with tribute.

Turning now to China, the famous House of Sung, the early years of which
were so full of promise of national prosperity, and which is deservedly
associated with one of the two most brilliant periods in Chinese
literature, was founded in 960. Korea was then forced, in order to
protect herself from the encroachments of China, to accept the hated
supremacy of the Kitans; but being promptly called upon to surrender
large tracts of territory, she suddenly entered into an alliance with
the Nü-chêns, who were also ready to revolt, and who sent an army to the
assistance of their new friends. The Nü-chên and Korean armies, acting
in concert, inflicted a severe defeat on the Kitans, and from this
victory may be dated the beginning of the Nü-chên power. China had
indeed already sent an embassy to the Nü-chêns, suggesting an alliance
and also a combination with Korea, by which means the aggression of the
Kitans might easily be checked; but during the eleventh century Korea
became alienated from the Nü-chêns, and even went so far as to advise
China to join with the Kitans in crushing the Nü-chêns. China, no doubt,
would have been glad to get rid of both these troublesome neighbours,