Why did Song China fall when Japan and Vietnam did not?

The short answer

• The problem of water. A fortress supplied by river could survive the passage of a mounted army nearby. The Song had many such defenses, set among wet fields where pasture was scarce. To maintain pressure, the Mongols needed control of waterways, siege equipment and ways to feed troops on rice. They acquired and built these capabilities over decades. The roughly 45-year war shows the effort needed to overcome a wealthy state whose defenses were tied to its rivers. Japan, across the open sea, would pose a different problem.
• Song resources and divisions. Commerce gave the Song money to pay armies and replace losses; defenders also used gunpowder weapons. These resources had to be directed through a court divided by politics. Chancellor Jia Sidao has been accused of concealing the state of the war, and commanders who joined the Yuan carried useful knowledge to the other side, including naval expertise. In the final years supporters of child emperors continued resistance from the coast. Song wealth sustained a long defense, but it could not ensure that the dynasty’s resources and talents would all serve it effectively.
• A claim to rule China. Military pressure could induce a commander to consider surrender. Khubilai’s Yuan title and Chinese forms of government gave him a further reason to do so: there might be a place for him in the new administration. Hangzhou was surrendered, occupied and taxed rather than stormed. Compare it with Merv. The two cases show different means available to Mongol rulers, and the value of retaining an administrative center that could continue to work.
• Expertise across long distances. The family wars placed demands on Mongol resources, including through Kaidu’s revolt (Ch. 9), yet expertise still traveled between distant regions. Engineers associated with the Ilkhanate contributed counterweight trebuchets at Xiangyang. Korean and Chinese shipbuilding and naval skills served Yuan campaigns, while Central Asian financiers worked in the empire. Khubilai could bring these different kinds of knowledge to bear against the Song despite division among Mongol rulers.

What it changed

A reunited China under the Yuan. The Yuan brought much of China under one dynasty after centuries of political division, with its capital at Beijing. Its authority also encompassed Yunnan, formerly the Dali kingdom, and extended into Tibet through distinctive arrangements. Later Chinese dynastic histories counted the Yuan among the legitimate dynasties. The Ming and Qing inherited parts of this political geography, although both institutions and borders changed.

A capital nearer the Chinese tax base. A court at Beijing was well placed to draw on north China’s population, officials and taxes. It was also farther from Karakorum and the politics of the steppe. Khubilai still had to contend with rivals there, including Kaidu and his long resistance. When the Yuan lost Beijing in 1368, Mongol rulers continued to govern on the steppe (Ch. 12). The location of the capital helped the dynasty use one source of power while leaving another set of relationships to manage.

Fleets for further campaigns. The Song war left the Yuan with fleets and sailors drawn from Chinese and Korean resources. Khubilai sent expeditions against Japan, Vietnam and Java, but possession of ships did not settle how each campaign would be supplied. The first invasion of Japan preceded Yamen; another followed in 1281. Chapter 11 follows the Yuan into these different settings and the difficulties they encountered there.