Song China covered most of the south of China. Once mightier, it had been reduced in size some centuries ago by Jin China. History started to diverge from OTL when the Mongols didn't conquer North China, so the Song had no opportunity to take some border provinces back. During 1268-79, there was obviously no Mongol conquest of Southern China. In 1274 (2971, Yang Wood Dog), Song Emperor Duzong died of natural causes. The new Emperor Gongdi was just five years old! Since 1300 (2997, Yang Metal Rat), Growing Nipponese piracy greatly hurt external trade of Song China.