In 1141, the Southern Song Dynasty and the Jin Dynasty entered into a peace agreement, known in history as the "Shaoxing Peace Conference". The Southern Song Dynasty ended a fourteen-year-long state of war between the two sides on the condition that they were vassals, cede land, and pay tribute to the Jin Dynasty. After the peace agreement was reached, the Jin Dynasty released Emperor Gaozong's biological mother, Concubine Wei Xian, and also handed over the coffin of Emperor Huizong of Song to the Southern Song side. During the Jing Kang Rebellion that year, Song Qinzong was also captured along with Emperor Huizong of Song, but he was unable to return to the south.
Emperor Qinzong of Song was named Zhao Huan (赵桓), the eldest son of Emperor Huizong of Song, and his biological mother was Empress Wang. In 1115, at the age of 16, Zhao Huan was made crown prince and succeeded to the throne ten years later, in other words, he was the orthodox emperor of the Song Dynasty. Emperor Gaozong of Song was the ninth son of Emperor Huizong of Song, and his biological mother was Princess Wei Xian. Although Zhao Zhuo was also a prince and was also given the title of Prince of Kang, he was not favored by Emperor Huizong of Song, similar to other princes. Without Jing Kang's change, Zhao Zhuo would not have been able to become an emperor in this lifetime!
After the Jing Kang Rebellion, Emperor Huizong of Song, Emperor Qinzong of Song, and other members of the clan all became prisoners and were taken to the north, where only Zhao Was not in the city. Therefore, in a sense, Zhao Shuo was the beneficiary of Jing Kang's change. Therefore, after the retreat of the Jin soldiers, Zhao Zhuo declared himself emperor in Nanjing, and rebuilt the Song Dynasty, which was called the Southern Song Dynasty. After a series of wars with the Jin Dynasty, Emperor Gaozong of Song found that the Jin Dynasty could not destroy the Song Dynasty at all, and it would not threaten his throne.
And it was Song Qinzong who threatened The Emperor Gaozong of Song, after all, he was the orthodox! At this time, Emperor Gaozong of Song also lost his fertility, and Emperor Qinzong of Song had several sons. Therefore, in this case, Emperor Gaozong of Song did not want Emperor Gaozong of Song to return to the south. When Emperor Gaozong of Song's birth mother, Princess Wei Xianfei, was about to return to the Southern Song Dynasty, Emperor Qinzong of Song grabbed her wheel and pleaded, "The first is to return to me, but it is enough for the lord of the Taiyi Palace, and there is no other hope for the Ninth Brother."
This incident also proves from the side that when Song Jin made peace talks, Song Gaozong did not ask for Song Qinzong's release at all. In 1143, Zhang Shao, an emissary of the Song Dynasty who had been detained by the Jin Dynasty, wrote a letter to Qin Juniper, "Saying that Jin has the intention of returning to yuansheng and the kings of the clan and advising him to send envoys to welcome him", Qin Juniper was furious. Qin Juniper had insight into Song Gaozong's psychology, and Qin Juniper's attitude was actually song Gaozong's psychology. In 1156, Emperor Qinzong of Song fell ill and died. Many years later, Song officials sent envoys to the Jin Dynasty, and the Jin Dynasty planned to hand over the coffin of Song Qinzong to the Song Dynasty, but was politely refused.
After talking about the reasons for the Southern Song Dynasty, let's take a look at your situation in the Jin Dynasty. After the war with the Northern Song Dynasty, the Jin Dynasty also realized that they could not destroy the Song Dynasty, but could only negotiate peace with the Southern Song Dynasty. However, the number of Jurchens was very small after all, and even though they occupied the Central Plains, the local people were still obsessed with the Southern Song Dynasty. Therefore, the rulers of the Jin Dynasty feared that once the Southern Song Dynasty regained its national strength, it would actively carry out the Northern Expedition, so that the Jin Dynasty would fall into passivity.
Therefore, Yan Zongbi (that is, Jin Wushu) insisted on detaining Song Qinzong, because in his view, Song Qinzong was a trump card against the Southern Song Dynasty! Once the Southern Song Dynasty broke the treaty and launched the Northern Expedition, the Jin Dynasty could use The orthodox position of Song Qinzong to support him as a puppet emperor to assist the Jin Dynasty in ruling the Central Plains. In this way, the war between Song and Jin became a contest between the brothers Of Song Qinzong and Emperor Gaozong of Song. Therefore, during this period, the Jin people were also reluctant to let Song Qinzong go.
After the death of Yan Zongbi, the Jin Dynasty basically abandoned this strategy, and no longer insisted on song Qinzong. However, Emperor Gaozong of Song remained negative on the matter, and although he sent emissaries several times on the surface, he did not make substantive representations. In 1156, Song Qinzong fell ill and died at the age of 57.
References: 1. "History of Song"; 2. "Records of the Year since Jianyan"; 3. "Compilation of the Northern League of the Three Dynasties"