Complex sentence: One of which was Beijing, which became a capital for the first time in its history, though it was not the principle capital of the dynasty, but rather was designated as the southern capital after the Khitan acquired the contentious Sixteen Prefectures in 935.
Split into simpler sentences: One of which was Beijing which became a capital for the first time in its history. It was not the principle capital of the dynasty but rather was designated as the southern capital after the Khitan acquired the contentious Sixteen Prefectures in 935.