Map showing the Song-Jurchen Jin wars
The Jin–Song Wars were a series of conflicts between the Jurchen Jin dynasty (1115–1234) and Han Chinese Song dynasty (960–1279). In 1115, the Jurchens rebelled against their overlords, the Khitan Liao dynasty (907–1125), and declared the formation of the Jin. Allying with the Song against their common enemy the Liao, the Jin promised to return to the Song the territories in northern China that had fallen under Liao control since 938. The Jurchens' quick defeat of the Liao combined with Song military failures made the Jin reluctant to cede these territories. After a series of failed negotiations that embittered both sides, the Jurchens attacked the Song in November 1125, dispatching one army towards Taiyuan and the other towards Kaifeng, the Song capital.
Surprised by the news of an invasion, the Song general stationed in Taiyuan retreated from the city, which was besieged and later captured. As the second Jin army approached the capital, Emperor Huizong of the Song abdicated and fled south. A new emperor, Qinzong, was enthroned. The Jurchens began a siege against Kaifeng in 1126, but Qinzong negotiated for their retreat from the capital after he agreed to pay a large annual indemnity. Qinzong reneged on the deal and ordered Song forces to defend the prefectures instead of fortifying the capital. The Jin resumed their war against the Song and again besieged Kaifeng in 1127. The Chinese emperor was captured in an event known as the Jingkang Incident, the capital was looted, and the Song lost northern China to the Jin. Remnants of the Song retreated to southern China and, after brief stays in several temporary capitals, eventually relocated to Hangzhou. The retreat of the Song court marked the end of the Northern Song era and the beginning of the Southern Song.
The Jurchens tried to conquer southern China in the 1130s, but they were bogged down by a pro-Song insurgency in the north and a counteroffensive by Song generals Yue Fei, Han Shizhong, and others. The generals regained some territories but retreated on the orders of the Southern Song emperor, who supported a peaceful resolution to the war. The Treaty of Shaoxing in 1142 settled the boundary between the two empires along the Huai River, but conflicts between the two dynasties continued until the fall of the Jin in 1234. A war against the Song begun by fourth Jin emperor, Wanyan Liang, was unsuccessful. He lost the Battle of Caishi (1161) and was later assassinated by his own disaffected officers. An invasion of the Jin motivated by Song revanchism (1206–1208) was also unsuccessful. A decade later, the Jin launched an abortive military campaign against the Song in 1217 to compensate for the territory that they had lost to the invading Mongols. The Song formed an alliance with the Mongols in 1233, and in the following year jointly captured Caizhou, the last refuge of the Jin emperor. The Jin dynasty collapsed that year in 1234. After the demise of the Jin, the Song dynasty itself became a target of the Mongols, and fell in 1279.
The wars engendered an era of technological, cultural, and demographic changes in China. Battles between the Song and Jin brought about the introduction of various gunpowder weapons. The siege of De'an in 1132 was the first recorded use of the fire lance, an early ancestor of firearms. There were also reports of battles fought with primitive gunpowder bombs like the incendiary huopao or the exploding tiehuopao, incendiary arrows, and other related weapons. In northern China, the Jurchen tribes were the ruling minority of an empire that was predominantly inhabited by former subjects of the Northern Song. Jurchen migrants settled in the conquered territories and assimilated with the local culture. The Jin government instituted a centralized imperial bureaucracy modeled on previous Chinese dynasties, basing their legitimacy on Confucian philosophy. Song refugees from the north resettled in southern China. The north was the cultural center of China, and its conquest by the Jin diminished the international stature of the Song dynasty. The Southern Song, however, quickly returned to economic prosperity, and trade with the Jin was lucrative despite decades of warfare. The capital of the Southern Song, Hangzhou, expanded into a major city for commerce.