Complex sentence: The Jurchens captured the main Khitan capital on February 23,1122, while their Chinese allies suffered a series of military defeats against the Liao and were forced to retreat twice back to the Song capital of Kaifeng.
Split into simpler sentences: The Jurchens captured the main Khitan capital on February 23,1122, while their Chinese allies suffered a series of military defeats against the Liao. They were forced to retreat twice back to the Song capital of Kaifeng.