Sixteen Prefectures
Relations between the Song and Liao (led by the Khitans) were relatively peaceful in the first two decades after Song was founded, the disputed territories of the Northern Han and the Sixteen Prefectures notwithstanding. In 974, the two began exchanging embassies on New Years Day. However, in 979 the Song moved against the Northern Han, long under the protection of the Liao dynasty. The Song emperor succeeded in forcing the Northern Han to surrender, but when marching on the Liao Southern Capital (present-day Beijing) in the Sixteen Prefectures, Song forces were defeated at the Battle of Gaoliang River. This defeat was politically damaging to the prestige of Emperor Taizong of Song (r. 976–997), so much so that his top military commanders orchestrated an aborted coup to replace him with his nephew Zhao Dezhao.