Mongol warriors’ traditional military advantages and cavalry tactics could not be fully deployed in their conquest of the Song dynasty. The Mongol Empire took more than 40 years to subjugate the Song but needed far less time to defeat other countries: they took Siberia in one year (1207), Qara Khitai (1216–1218) and Khwarazm (1219–1220) in two years each, the Western Xia empire in 21 years (1205–1227) and the Jin empire in 22 years (1211–1234).
From 1235–1278, the Mongols launched three large-scale military campaigns against the Song. Their early raids on the Song were not conducted by their elite forces, who were at that time engaged in plundering and sacking communities across Europe. The Middle Kingdom, unlike Europe and Central Asia, did not have the same vast regions of grassy plains which played into the hands of the masters of the steppe. China nevertheless had a booming economy, fuelled by a prodigious number of exports to Central Asia, Southeast Asia, Korea, Japan and even as far as Africa, ranging from silk, tea and porcelains to printed books, paper and copper coins. In addition to its strong agricultural base, the Song therefore had plenty to rely on to sustain a long-term battle. The Mongols favoured winter for their campaigns as the season had the climate closest to that of their inhospitable homeland upon which many of their ground tactics had been developed. However, although they might open their military campaigns against the Chinese Song in winter, the campaigns often dragged on through the summer when the Middle Kingdom was so sultry that neither the Mongolian horses nor the men could cope with the heat. Worse still, the conditions encouraged epidemics to spread in the Mongol camps.
The Mongols came particularly unstuck by the major and critical battles that took place in Sichuan and Xiangyang, Hunan, where naval rather than cavalry forces and tactics were most needed. This was also their Achilles heel that led to their failed expeditions against Vietnam and Japan.
Helped by the recruitment of Pu Shougeng, a Muslim defector who had been in charge of the Song’s maritime affairs for 30 years, the situation changed. Pu Shougeng handed over all the Song’s warships to the Mongols and helped to build another 600. With this addition of naval hardware, the Mongols made great tactical strides. Finally, exacerbated by internal political conflict, the Song was toppled by Genghis Khan’s grandson Kublai (1215–1294) who proclaimed the Yuan dynasty in 1279. The Yuan was the first alien dynasty in Chinese antiquity