Following their secret 'Alliance on the Sea' to destroy the Liao Dynasty, the Song Dynasty displayed profound military weakness during the joint campaigns. Tensions escalated further when the Song delayed the agreed-upon tribute payments, secretly welcomed the defected Jin governor Zhang Jue, and exchanged secret correspondence with the fleeing Liao Emperor Tianzuo to plot a joint attack. Viewing this as a complete betrayal of their alliance, the Jurchen Jin Dynasty turned its armies southward in 1125. The Jin forces rapidly swept through the Central Plains and besieged the capital, Kaifeng. This culminated in the devastating Jingkang Incident in 1127, where Emperor Qinzong, his father Huizong, and thousands of nobles were captured and dragged north, bringing the Northern Song Dynasty to an end.
Amidst the catastrophic fall of the capital and the capture of the entire royal court, Prince Zhao Gou (Emperor Gaozong), the ninth son of Huizong and younger brother of Qinzong, was the only imperial prince to evade capture as he had been stationed outside the besieged city. As the sole surviving direct descendant of the Northern Song imperial bloodline, Zhao Gou gained the support of surviving officials and the populace, fleeing south to establish the Southern Song Dynasty at Lin'an (Hangzhou) and ascending the throne. The Jin launched relentless campaigns to wipe out the remaining Song forces, attempting to cross the Yangtze River. However, Song forces led by generals like Han Shizhong utilized the southern rivers and lakes, resisting the Jin fleet at the Battle of Huangtiandang. While they could not completely defeat the powerful Jin cavalry, these naval defensive operations made it difficult for the Jin to secure control of the southern lands, enabling the Southern Song to establish a stable foothold in Jiangnan.
By the late 1130s, general Yue Fei and other military commanders strongly pushed for Northern Expeditions to reclaim the lost Central Plains and rescue the captured emperors, Huizong and Qinzong, to restore national dignity. Yue Fei's army achieved significant tactical successes, defeating the Jin cavalry at the Battle of Zhuxianzhen and nearing the old capital of Kaifeng. However, Emperor Gaozong and chancellor Qin Hui, representing the pro-peace faction at court, held different views. They argued that prolonged warfare had depleted state finances and exhausted the populace, making peace necessary. Furthermore, Emperor Gaozong feared that the return of the former emperor Qinzong would threaten his own legitimacy on the throne, while the court was deeply concerned about military commanders growing too powerful and forming autonomous warlord factions. Believing that diplomatic compromise was the only realistic way to ensure the dynasty's survival, the court ordered Yue Fei to withdraw.
Ultimately, Yue Fei was recalled to the court and executed on trumped-up charges of treason. In 1142, the Treaty of Shaoxing was signed between the Song and Jin dynasties. Under this agreement, the Southern Song ceded all northern territories to the Jin, establishing the Huai River as the official border, and agreed to pay substantial annual tributes as a subordinate state. Although the treaty forced the Song to accept humiliating terms and the permanent loss of the Central Plains, it successfully brought an end to decades of devastating warfare, allowing both empires to enter a period of relative stability and cultural prosperity within their respective borders.
