The Jin Dynasty grew stronger and stronger under the leadership of Yan Akuta, realized the great cause of destroying the Liao dynasty and the Song Dynasty, and was known as the title of "Jurchen dissatisfied with ten thousand, full of invincible". However, after the Jin State destroyed the Liao State, it failed to take advantage of the strong army to conquer the Mongolian plateau previously ruled by the Liao State, and directly let Genghis Khan sit on the throne.
In 1125, the Jin army captured Emperor Tianzuo of Liao at Jiashan, and the Liao state collapsed. The Murwei tribe, which had originally been attached to the Liao state, was preparing to surrender to the Jin state. However, since the beginning of the following year, the main force of the Jin army has gone south to attack the Song, and the star lineups such as Yan Zongwang, Zong Han, Zong Pan, and Zong Bi have all gone to fight the Song, and not many troops have been allocated to manage the Mongolian steppe. Among them, the leader of the Qiyan tribe, Bo'er Jin Hebule, led his troops to break away from the jurisdiction of the old Liao, established themselves on the steppe, and became the new Mongol tribe, and was elected as Hebul Khan. When Hebul Khan invaded the Jin state in 1139, when a group of famous generals of the Jin state were still facing Han Shizhong, Wu Jiu, Zhang Jun, and others in the south, Jin Xizong had to send Hu Shahu (not the powerful minister Hu Shahu in the late Jin dynasty) to go with more than 10,000 cavalry to conquest the Qiyan tribe, but hebul Khan lured the enemy deep into the Mongolian steppe, interrupted the logistics line, and then divided and defeated. This is also the prototype of genghis Khan's later tactics. The Jin army fought the Song army on the southern front for more than ten years, during which time it sent an army to the northwest to pursue Yelü Dashi, who established the Western Liao regime, but was repelled by the other side. After the Song court recalled Yue Fei's Northern Expeditionary Army and signed the "Shaoxing Peace Agreement", the Jin State freed up its hands to clean up Mongolia. However, some of the famous generals of the Jin Dynasty died of illness, some died of war, some died of political struggles, and the most powerful general who survived was Yan Zongbi, that is, Jin Wushu.
So in 1146, Jin Xizong sent Jin Wushu to lead an army of 80,000 to conquer Hebul. When Jin Wushu went out on the expedition, he specially left a third of his army to defend the logistics transportation line to avoid being harassed by the Mongol Rangers. Hebule used the method of luring the enemy to go deep and cutting off the enemy's grain road against the Jin army, but they were all defused by the Jin Wushu. It was difficult for Hebule to defeat the Jin army from the front, so he took advantage of the strategic depth of the vast Mongolian steppe to play a guerrilla war with Jin Wushu. Although the Jin army was able to defeat the Mongol army in almost every field battle, it failed to eliminate the enemy's living forces in large numbers, and the other side was always able to gather new forces to harass itself. In the end, the two sides reached a collegial agreement: the Jin State ceded Xiping, Hebei and other 27 tuanzhai villages to the Mongols, gave some rice noodles cattle and sheep every year, and in 1148 crowned Bule Khan as the King of the Mongols, that is, the King of Mongolia. Through this incident, Jin Wushu realized that the active attack on the Mongols would not solve the problem, or imitate the Central Plains Dynasty to build the Great Wall. So the Golden Wall was built on the border near Mongolia. After Jin Shizong completed Yan Yong's ascension to the throne, he made great efforts to repair relations with neighboring countries and let the national strength of Jin Guo reach its peak, known as "Northern Yao Shun". At the same time, continuing to strengthen the Great Wall, Xia Ming set up a border fort of seventy at the border of Taizhou and Linhuang, and stationed 13,000 troops. The power of the Jin state went from peak to decline in the hands of Jin Zhangzong. After becoming Genghis Khan of the Great Mongol State, Temujin wanted to conquer the Jin Dynasty in the south. However, the yuwei of Jin Shizong and Zhangzong was still there, making it difficult for Temujin to make it difficult for him to make a decision to march south. When Emperor Zhangzong died, Temujin learned that the throne was completed by The King of Wei Shao, who he had always looked down upon, and said with a smile: "I say that the Emperor of zhongyuan is a heavenly man, and such a cowardly is also for it. And a few years later, a gold war was launched.
The main reason why the Jin Kingdom failed to swallow Mongolia at its peak was that the Jurchens were a semi-fishing, hunting, and semi-farming people scattered in the northeast, unable to garrison enough troops and populations on the Mongolian plateau to maintain their rule over Mongolia, and the nomadic and fishing/farming areas were bounded by the Golden Great Wall, and it was difficult for the Jin State to cross this line to actually rule the Mongol tribes, and could only adopt a bondage approach.
Secondly, most of the elite generals in the early Jin Dynasty were consumed in the battlefield against the Song Dynasty, and the strength that could be used when conquering the Mongols was much worse than before. In addition, the Mongols themselves are brave and good at war, have a unique survival wisdom, and are not so easy to deal with. So it is not surprising that the Golden State could not swallow Mongolia at its peak.