Song rulers had some domain south of the Yangtze River that had most of the empire’s population and big merchant cities. When the Southern Song Dynasty started, it was decided that improvements had to be made. The government had ships built and improved harbor facilities for merchants. The cities of Quanzhou, Guangzhou and Xiamen were big seaports and were very successful because the government also built a navy that protected merchant ships all the way to India or even Arabia. Due to this success in trade, the empire continued to prosperous.

The Jin Empire that defeated the Northern Song was also out to defeat the Southern Song but the Southern Song were stronger and withstood all of the attacks. Also, the Southern Song had a better navy than the Jin so the Jin’s attacks were futile in proportion of size and quality. Since the Southern Song were south of the Yangtze River, the river was a successful natural and defensive boundary due to its width.

The Song weren’t the only ones who wanted to fight the Jin though. The Mongols attacked the Jin and the Western Xia and near the end of the Song Dynasty, the Southern Song allied with the Mongols and they attacked the Jin Empire. When the Jin Empire was defeated, the Southern Song reclaimed the cities of Kaifeng and Beijing but the Mongols under Kublai Khan attacked the Song. After nearly two decades of fighting, the Song capital was taken in 1279 and the Song era ended.