The battle was fought in three stages between March and October 1211, as soon as the Mongol army went past through the Great Wall with little opposition.
Battle of Wusha Fortress The Jin
chancellor,
Duji Sizhong (獨吉思忠), led the bulk of the Jin army to the northwestern frontline. The Jin could not match the numbers of Mongol horsemen, and had only 30,000–50,000 troops. The chancellor sent troops to reinforce the defenses along the
Jin dynasty's Great Wall and prevent the Mongols from advancing further south. Genghis Khan ordered his third son,
Ögedei to lead a separate force to attack the Jin western capital, Xijing (西京; present-day
Datong,
Shanxi), and block enemy reinforcements. The Khan himself led the main Mongol army to attack Wusha Fortress (烏沙堡) and capture Wuyue Camp (烏月營), thus destroying the Jin army's defence lines. Duji Sighing was killed in action and most of the Jin army was wiped out. This battle took place between March and the end of June 1211. The Mongols then rested for about a month before moving towards Yehuling and sending an ambassador to meet the Jin imperial court.
Battle of Yehuling and Huan'erzui Wanyan Chengyu (完顏承裕), who succeeded Duji Sizhong as chancellor, was put in charge of the Jin army. He ordered his men to abandon the three cities of Hengzhou (恆州; in present-day
Zhenglan Banner,
Inner Mongolia, Changzhou (昌州; north of present-day Jiuliancheng Town,
Guyuan County,
Hebei), Fuzhou (撫州; present-day
Zhangbei County, Hebei), and move towards Yehuling. His aim was to make use of the mountainous terrain in Yehuling to obstruct the Mongol cavalry. Mountainous terrain was a challenge for the Mongolian cavalry. However it was also a difficult area to fight in for the bigger Jin forces. The vast Jin forces were scattered among the mountains and the valley choke points. The difficult terrain and far distances made communication and coordination of troops difficult. This would prove fatal for the Jin forces, when the Mongols executed a focused and concentrated attack. The Jin imperial court sent
Shimo Ming'an (石抹明安), an official of
Khitan descent, to meet Genghis Khan and start peace negotiations. However, Genghis Khan managed to induce Shimo Ming'an to surrender and defect to his side. Shimo Ming'an even provided the Mongols with military intelligence about the Jin army. Genghis Khan sent his general
Muqali to lead the Balu Unit (八魯營) to launch a surprise cavalry charge on the enemy via a passage at Huan'erzui (獾兒嘴; lit. "Badger Mouth"). Before the battle, Muqali promised Genghis Khan, "I will not return alive if I do not defeat the Jin army!" The Mongol army's morale surged. Because of the mountainous terrain, the Mongols were unable to deploy their superior cavalry to its full advantage, hence they dismounted and fought on foot. High on morale, the Mongols defeated the central Jin forces and fought their way towards Wanyan Chengyu's main camp. Due to poor communications, the Jin forces on the sides were not able to reinforce the central Jin positions. Eventually, the Jin army became disorganized, lost its morale, and started to break. The Jin army's field commander, Wanyan Jiujin (完顏九斤), was killed in action. With the collapse of the central Jin forces, the other Jin forces nearby soon routed and a massacre followed. The entire Jin army was destroyed, leaving dead corpses for over a hundred miles. This battle took place in August 1211.
Battle of Huihe Fortress Wanyan Chengyu managed to rally the scattered Jin forces after the Battle of Huan'erzui and Yehuling and gather at Huihe Fortress (澮河堡). However, they soon came under attack by pursuing Mongol forces around October 1211. The Mongols swiftly surrounded the Jin forces and engaged them in fierce battle for three days. Genghis Khan then personally led 3,000 horsemen on a cavalry charge towards the enemy while the remaining Mongol forces followed behind. The entire Jin army was destroyed while Wanyan Chengyu barely escaped alive. Wanyan Chengyu was replaced by
Tushan Yi (徒單鎰) as chancellor. ==Aftermath==