Analysis of information sources in references of the Wikipedia article "Cao Ly Hiển Tông" in Vietnamese language version.
From 1015 to 1019 there was incessant warfare, with attacks on Koryŏ in 1015, 1016, and 1017 in which victory went sometimes to Koryŏ, sometimes to the Khitan, but in sum were indecisive.
In 1018 a huge new expeditionary force was mobilized by the Khitan and placed under the command of Hsiao P'ai-ya. The army crossed the Yalu late in 1018 but was ambushed by a superior Koryŏ force, suffering severe losses. The Koryŏ army had also cut their line of retreat, and so Hsiao P'ai-ya marched south, planning to take the capital Kaegyŏng, as in 1011. But this time the Koreans had prepared defenses around the capital, and the Khitan, constantly harried by Korean attacks, were forced to retreat toward the Yalu. At Kuju, between the Ch'a and T'o rivers, they were encircled and attacked by the main Koryŏ forces, which almost annihilated the Khitan army. Only a few thousand men managed to return to the Liao border. This was by far the worst defeat suffered by the Khitan during Sheng-tsung's reign, and in consequence Hsiao P'ai-ya was stripped of all his titles and offices and disgraced.
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