As a dynasty established by the Jurchens, the Jin Dynasty has a strong mark in history, because they have the shame of Jingkang of the Song Dynasty. However, the Jin Dynasty, like other regimes, went through the establishment of the state, to its prosperity, to its decline, and finally to its demise. Their demise was hugely linked to the rise of the northern Mongolia.
Speaking of Mongolia, we cannot fail to mention the generation of Tianjiao Genghis Khan, who established the Great Mongolia State, and in addition to destroying the Jin Dynasty during his lifetime, his greatest achievement was to launch a western expedition to make the territory of the Great Mongolia span the Eurasian continent.
After Genghis Khan's son unified the Mongolia tribes, he established the Great Mongolia State and began to break away from the control of the Jin Dynasty, waging several Mengjin wars. The Jin dynasty was no match for the Mongolians at all, lost large swaths of territory, and eventually sued for peace with the Mongolians.
Genghis Khan originally planned to complete the unification of the Central Plains first, but because of a dispute with Khorezm, he chose to march west. It stands to reason that the Jin Dynasty should take advantage of Genghis Khan's western expedition to quickly rest and recuperate, restore national strength, and form alliances with the Southern Song Dynasty and Western Xia through diplomacy to jointly deal with the next Mongolia attack. But Kim Xuanzong did not do this at that time, and the decision he made was both surprising and reasonable at the same time.
So what exactly did Kim Xuanzong decide?
After winning the Mengjin War, Mongolia was very strong, but Genghis Khan took most of the combat power with him in order to conquer the west. In order to deal with the Central Plains Dynasty, he named Mu Huali as the "King of Taishi", leaving a part of the army, allowing him to act at the opportunity and decide on his own matters of the southern expedition.
After that war, the strength of the Jin Dynasty was greatly damaged, and Jin Xuanzong moved the capital to Bianjing for safety, which caused panic among the people in the north. Later, Puxian Wannu, who was in charge of garrisoning the north, established himself in Liaodong and betrayed the Jin Dynasty.
Even if the Jin Dynasty was weak, Mu Huali had no intention of going south at that time, because the number of troops left by Genghis Khan was too small, only 10,000 Wang Gubu and 12,000 Mongolia Tanma Red Army, and the rest were composed of Han and Khitan people, with a total of only 100,000 people.
Therefore, this period is the best time for the Jin Dynasty to restore its national strength.
However, Kim Xuanzong did not do this. The Southern Song Dynasty and the Jin Dynasty can be regarded as a feud, although there have been many peace discussions, but they are still fighting each other. In the second year of the Kaixi of the Southern Song Dynasty, they took advantage of the rise of the Mongolia to launch the Kaixi Northern Expedition against the Jin Dynasty, but ultimately failed. This incident made Jin Xuanzong understand that the military strength of the Southern Song Dynasty was still weak, so he planned to attack the Southern Song Dynasty. He believed that the Jin Dynasty was indeed inferior to the Mongolia, resulting in the loss of a large amount of territory, but it could also bully the Southern Song Dynasty. As long as the land is taken from the hands of the Southern Song Dynasty, or even the other party is destroyed, it can completely make up for what the north has lost.
In fact, the Jin Dynasty at that time not only launched the southern expedition, but also launched many attacks on the Western Xia, with the same purpose as the southern expedition. At the same time, they also took advantage of Genghis Khan's westward expedition and the emptiness of the north to launch the Northern Expedition.
The final struggle of the Jin Dynasty did allow them to take a large part of the territory, but it was this attack that consumed the remaining national strength. The Mongolia did not give the Jin dynasty time to regain its national strength, and after Genghis Khan returned from his western expedition, he launched an attack on the Jin dynasty. However, in 1227 AD, a generation of Tianjiao died of illness, giving the Jin Dynasty a chance to breathe.
After Ögedai Khan succeeded to the throne, he united with the Southern Song Dynasty to attack the Jin Dynasty and successfully overthrew it.
Although it is said that at the time of Genghis Khan's westward expedition, the idea of the vast majority of people must be to take this opportunity to quickly restore the national strength, but Jin Xuanzong's idea is to make up for what was lost before through war. This is indeed in line with the Jurchen people's approach, and his goal has indeed been achieved, but it is a pity that there is no extra time for the Jin Dynasty. The previous wars further depleted the country's strength, which hastened the demise of the Jin Dynasty.