In 1217, at the site of Kaifeng, Jin Xuanzong made a decision that since he could not win the Mongols, it was better to attack the Southern Song Dynasty and make up for the losses in the war against the Mongols. The strategy of "making up for the loss of the north and making up for the south" was a bad decision of Jin Xuanzong, which accelerated the pace of the demise of the Jin kingdom and the demise of the Southern Song Dynasty.
In 1206, Temujin held the Kuriletai Assembly on the banks of the Nannan River and established the Mongol Khanate, known as "Genghis Khan". Next, Genghis Khan swept through the various princes, unified the Mongolian steppe, and began to wage war against the Jin Dynasty. For Mongolia, internal cohesion can only be ensured by constant conquest and acquisition of the necessary supplies of subsistence.
In 1211, Genghis Khan ordered 150,000 troops to attack the important towns along the border of the Jin State, and then attacked Shanxi all the way and Hebei all the way, and the Pressure of the Jin State was very high. The Battle of Wild Fox Ridge, the Battle of Yanjing, the Battle of Shanxi, and the Jin Dynasty were all defeated and lost 400,000 soldiers and horses. More crucially, the Mongols seized hengzhou, a horse farm, and the Jin dynasty lost a million warhorses, and the cavalry was severely weakened.
In order to avoid the Mongol advances, Jin Xuanzong abandoned Yanjing and moved to Kaifeng, Henan, in order to "move south for Zhenyou". In Genghis Khan's view, the Jin State violated the agreement, so it once again went south and swept through all parts of the Central Plains, and the Jin State was seriously injured. In this way, Jin Xuanzong planned to get compensation from the Southern Song Dynasty and planned to send troops south.
When Genghis Khan established the Mongol Khanate, the Southern Song Dynasty was also active, fighting against the "uncle" Jinguo. In 1206, the Southern Song Dynasty minister Han Nongxin restored Yue Fei's name and posthumously created him "King of E" to win the support of the anti-resistance faction. Next, Han Nongxin ordered 150,000 troops and divided into three ways to attack the Jin Dynasty in an attempt to wash away the "shame of Jingkang".
Han Nong's Northern Expedition to the Central Plains, Xin Abandoned Disease was not optimistic, thinking that he was blindly tossing and turning, and he sent troops without any preparation, and the probability of failure was very large. So Xin Abandoned Disease wrote a poem, "Yuan Jia Grass Grass, Seal the Wolf Juxu, win the Emperor Beigu." This means that Han Nongxu will repeat the mistakes of Emperor Wen of Song, lose soldiers and generals, and beg for bitter food.
In the "Kaixi Northern Expedition" in 1206, the Song army was defeated, losing tens of thousands of elite troops, and the famous general Wu Xi surrendered to the Jin state. Han Nongxu also wanted to continue the Northern Expedition, and as a result, Shi Miyuan gave his head to the Jin State as a "letter of surrender" for the peace. The Song army failed in the Northern Expedition and once again made a compromise with the Jin Kingdom, increasing the number of coins to 300,000 taels and the cloth to 300,000 horses, and renaming the Jin Kingdom "Uncle".
When the Northern Expedition failed, the Jin State saw the weakness of the Southern Song Dynasty, the Song soldiers were numerous, but the combat effectiveness was not good, and the emperor did not have the will to fight. In the Battle of Qinzhou, 30,000 Song troops were killed, and Gao Qi, the shuhu, led 2,000 Jurchen cavalry to counterattack, beheading more than 4,000 people and taking hundreds of prisoners. The Song Army did not give strength, and it was no wonder that Jin Guo looked down on it, after all, the strength was there.
When Genghis Khan went south, the Jin Dynasty was defeated, and the Southern Song Dynasty kept an eye on the development of the situation. After the Battle of Wild Fox Ridge, the elite troops of the Jin Dynasty were lost, and the Southern Song Dynasty "did not talk about martial virtue" and stopped paying the Annual Coin to the Jin State. In addition, the court of the Southern Song Dynasty even had the intention of joining forces with Mongolia to deal with the Jin Dynasty. At that time, Emperor Huizong of Song did the same, signing the "Alliance on the Sea" with the Jin State to deal with the Khitan together.
The Southern Song Dynasty stopped paying the old coins, and the Jin Xuan Sect sent people to question them, but they were discouraged. In 1217, Genghis Khan put Muhuali in charge of the military affairs of southern Mo, and he himself led 150,000 cavalry to the west to attack Hua lazimo. At this time, the pressure on the north of the Jin Dynasty was reduced, and Jin Xuanzong decided to implement the battle plan of "making up for the loss of the north and making up for the south", sending 200,000 troops to attack Jianghuai and Sichuan, and the Jin-Song War broke out again.
The battle plan of "making up for the loss of the north and making up for the south" was a bad decision of Jin Xuanzong. With 200,000 troops heading south, Mu Huali did not relax his attack on the Jinguo, and the Jinguo fell into a passive situation of two-front combat. The Mongol cavalry defeated the Jin army of 100,000 at Shanxi, and one of the Mongols attacked Guanzhong. In the southern battlefield, the Jin Kingdom did not progress smoothly, and was blocked from Xiangyang by the Song army.
The Jin army went south, and in order to resist the enemy, the Southern Song Dynasty sent people to contact Genghis Khan and promised to lend the Way to the Mongol army and let them attack the Jin State from behind. In 1232, Tuolei led 50,000 elite troops through the territory of the Southern Song Dynasty, and then joined the main force of Wokoutai at Sanfeng Mountain, annihilating 130,000 Jin soldiers.
In the Battle of Sanfeng Mountain, Jin Guoyuan was seriously injured. Wu Xian, a famous general of the Jin Kingdom, led more than a dozen people to break out after the Battle of Sanfeng Mountain, and then went to Henan to collect the defeated troops and get 100,000 soldiers and horses. At this time, Jin Aizong did not forget to attack the Southern Song Dynasty and continue the battle plan of "losing the north and making up for the south", and Wu Xian led an army of 100,000 to attack Sichuan, suppressing the Song army and hanging.
Wu Xian marched into Sichuan, and the Song army was defeated until he met the famous general Meng Jue. 100,000 Jin soldiers went south, with the goal of capturing Sichuan and establishing a base area. Meng Jue ended Wu Xian's dream, 100,000 Jin soldiers were completely destroyed at Mount Madeng, and Wu Xian fled back to Cai Prefecture and held the city with Jin Aizong. At this time, the Jin Dynasty was isolated, and there was only one isolated city in Caizhou, and its demise was inevitable.
In 1234, Meng Jue led 20,000 troops to fight with the Mongols and conquer Caizhou. Less than an hour after the new succession, Yan Chenglin was killed in battle, and Jin Aizong hanged himself at Youlanxuan, and was divided into two halves by Meng Jue, part of which was given to the Mongols and part of which was transported back to Lin'an. Caizhou fell, the Jin Dynasty perished, and the Southern Song Dynasty finally washed away the "shame of Jingkang".
After the fall of the Jin Dynasty, there were differences between the Southern Song Dynasty and the Mongols, and the Southern Song Dynasty took the initiative to send troops to the Northern Plains to recover the lost land. As a result, everyone knows that in the "Duanping into Luo" incident in 1234, the Southern Song Dynasty betrayed its faith and ventured against the enemy, losing 50,000 elite soldiers, opening the prelude to the Song-Mongolian War.
Without the Jin Dynasty as a buffer, the Southern Song Dynasty itself did not give strength, and could only kill itself. In 1276, the Mongol army arrived in Lin'an, and Empress Xie surrendered to Kublai Khan with Emperor Gong of Song. In 1279, Zhang Hongfan led the Mongol cavalry and the "Han Army" sailors to attack Yashan, Lu Xiufu committed suicide by jumping into the sea with the little emperor on his back, 100,000 soldiers and civilians also jumped, and the Southern Song Dynasty fell.
It can be said that the battle plan of "making up for the loss of the north and the south" was a bad decision, and neither the Jin Dynasty nor the Southern Song Dynasty were beneficiaries. The Southern Song Dynasty stopped supplying coins, and Jin Xuanzong thought that the Song army would be easy to fight, so he adopted the plan of "making up for the loss of the north and the south" of the Shuhu Gaoqi. As a result, the Southern Song Dynasty joined forces with the Mongols and destroyed the Jin Dynasty. Without the Jin Dynasty as a buffer, the Mongol cavalry swept through the Southern Song Dynasty and unified the Central Plains.
Bibliography: History of the Song Dynasty