Battle of Huan'erzui

The Battle of Huan'erzui (the Campaign of the Badger Mouth and Wild Fox Peak) was the major decisive battle in the first stage of the Mongol conquest of the Jin dynasty.

Background
In 1210, Genghis Khan insulted Prince Shao of Wei, ruling as Emperor Weishaowang of Jin, by publicly stating that he was a coward and unfit to be a leader. Genghis added, "The emperor should be a man from sky like me." Soon, news spread to the Jin emperor through a Jin officer. The Jin emperor was enraged and ordered the execution of the Mongolian ambassador. Tensions between the Jin and the Mongols started to escalate and Genghis Khan declared war with the Jin. The Mongolian army amassed 90,000 men for the offensive force in the expedition against the emperor in March 1211. Genghis Khan only maintained a defending force of 2000 guards in Mongolia. This means that well over 90% of the available forces in Mongolia at the time were mobilized for this campaign. Before the expedition, Genghis Khan conducted a religious ritual with his troops by praying to Tengri along the Kherlen River for victory and made a vow to avenge his ancestor, Ambaghai Khan, who was betrayed by the Tatar and executed by the Jin court.

Jin army
The Jin army included:

1. Border troops: recently defeated by Mongolia at the Battle of Wushabao several months before the campaign, the border troops had withdrawn to Badger Mouth. Their total strength amounted to 100,000 and were led by 1st Prime Minister Du Qiannu.

2. Main troops: their strength amounted to 250,000 and chief commander of the army was field marshal Wanyan Chenyu, 2nd Prime Minister and general Ming An. Most of the troops hailed from the capital.

3. Reinforcement troops: emergency troops from all corners of Jin country, their strength amounted to 150,000 and the commander was vice field marshal Hersle Whosawho, an ambitious man. He was to defend Datong with his reinforcements.

Battles
This campaign included a series of five battles that took place from May to October, 1211:

1. Battle of Wushabao (烏沙堡戰役): May–June.

2. Battle of Datong (大同攻防戰): lasted seven days in August.

Genghis Khan ordered his three elder sons and general Yelü Tuhwa into battle. Each of his sons commanded 10,000 cavalry. A total of 30,000 cavalry besieged the city in order to cover the side line of the Genghis Khan's troops and cut off Jin's reinforcements to capital.

3. Huan'erzui and Yehuling Campaign (獾兒嘴及野狐嶺戰役): occurred in August.

This pass leads directly to Jin's capital and was attacked by Genghis Khan with a commanding force of 60,000.

4. Battle of Guihebao (澮河堡戰役): happened in October and the combat lasted three days.

5. The Mongol occupation of Juyong Pass:

Jin's 3rd Prime Minister Tu Danyi (徒單鎰) successfully defended the capital with a commanding force of 20,000, signalling the end of the campaign.

Battle of Wushabao
Wusha Fortress is located at the present city of Ulanqab. Through the years, Jin's 1st Prime Minister Dujis Qiannu ordered the construction line of a series of single fortifications to oversee the Mongols, but this tactic turns out to be faulty, even though they maintain their stability on the border. Wushabao was one of the largest and most important fortresses at the time.

Jebe attacked Wushabao and achieved no success. He changed his tactics by attacking Wushabao's reinforcement base. With the fall of the base, Jebe manage to capture Wushabao. Hearing the news, a senior official of Jin (a rank below prime minister) led the troops into retreat from the neighboring three counties to Badger Mouth. The retreat provided a golden opportunity for Jebe and soon the three counties were captured with ease.

Battle of the Huan'erzui (Badger's Mouth)
To combat the Mongol advance, the Jin withdrew soldiers from cities for hundreds of miles, resulting in a combined force of approximately 400,000 to 500,000 soldiers being stationed at Huan'erzui. However, the Jin were overly confident in the defensive position of the pass; Genghis eventually circumvented Jin defenses by sending his men over the peaks surrounding the pass, allowing him to encircle the much larger Jin army. As Genghis attacked the front of the Jin army at the entrance to the pass, his forces simultaneously routed the Jin cavalry from behind. The encircling force then proceeded to attack the supply camps in the rear of the Jin army, resulting in the slaughter of many resting Jin soldiers. When Jin forces in the front lines of the battle were eventually pushed into retreat by the bulk of the Mongol army, the subsequent chaos resulted in the slaughter of even more Jin soldiers.

Following the battle, the general of the Jin army retreated to the central Jin capital of Zhongdu (modern Beijing) and assassinated the emperor, and assumed control of the city. After a four-year Mongol siege, which saw the residents of Beijing reduced to cannibalism in order to survive, the city finally surrendered. The Jin were allowed to retain control of Zhongdu, but were forced to pay a large tribute in return. The following summer, Emperor Xuanzong of Jin abandoned Zhongdu and moved the government to the "southern capital" of Kaifeng. While the Jin maintained a grasp on power for several more years, the empire was severely weakened, and eventually capitulated to a combined Mongol and Southern Song force in 1234.

Aftermath
After this battle and campaign, the Jin dynasty lost half of its 950,000 troops. Roughly ten Jin cities were plundered by the Mongols and Genghis Khan ordered a tribute of 500 males, 500 virgins and 3000 horses to be taken back to the Mongolian plains.

In spite of the defeat, Jin prioritized conquering the Song dynasty over defending its borders against future Mongol incursions and invasions.