During his campaign against the Oirat, Emperor Yingzong of Ming was captured in the Tumu Crisis. The Ming then organized defenses and rearranged power at court. The consequences extended beyond a battlefield defeat to the accession of a new emperor, the defense of Beijing, and Yingzong's later return to the throne.

Historical background

The Tumu Crisis, also known as the Crisis of the Tumu Fortress, or the Jisi Incident, was a border conflict between the Oirat Mongols and the Ming dynasty of China. In July 1449, Esen Taishi, leader of the Oirat Mongols, launched a large-scale, three-pronged invasion of China. Despite having capable generals, Emperor Yingzong of Ming, under the influence of eunuch Wang Zhen who dominated the Ming court at the time, made the decision to personally lead his armies into battle against Esen. On 1 September, the Ming army suffered a crushing defeat at the hands of the much weaker Mongols, and the Emperor was captured. This defeat was one of the biggest military failures in the Ming dynasty's three centuries of existence, and it was largely attributed to the poor leadership of their army.

Esen was not prepared for the scale of his victory or for the capture of the Ming emperor. Initially, he attempted to use the captured Emperor to raise a ransom and planned to conquer the undefended Ming capital of Beijing. His plan was foiled due to the steadfast leadership of the commander in the capital, Yu Qian, and the ascension of the captured Emperor's brother, the Jingtai Emperor. Emperor Yingzong was eventually released in 1450, but his brother placed him under house arrest.

Military situation

The Ming dynasty was established in China in 1368 when Zhu Yuanzhang (the Hongwu Emperor), a former peasant rebel, overthrew the Mongol-led Yuan dynasty and forced the Mongols to retreat back to the northern steppes. To counter persistent Mongol threats along the northern frontier, the Hongwu Emperor implemented significant military reforms and launched multiple military campaigns to secure the border regions. His son, the Yongle Emperor, further expanded these efforts by personally leading expeditions against the Mongols between 1410 and 1424. The decision to move the capital to Beijing in 1421 was also a strategic move to focus on northern defense. While these aggressive policies initially strengthened frontier security, they ultimately depleted Ming resources.

After the death of the Yongle Emperor in 1424, the defense of the northern borders began to deteriorate. Despite complaints from generals about the lack of resources, no action was taken. In 1435 and 1438, some garrisons were reinforced, but the overall situation remained unchanged. Inland, only half of the supposed 2.5 million soldiers in the Weisuo military system were actually performing their duties.

Tumu debacle

Esen dispatched troops to block Chinese access to the river south of their camp. By the morning of 1 September, the Mongols had surrounded the Chinese camp and offered to negotiate. Wang Zhen ignored their overtures and instead ordered the confused Ming army to advance towards the river. A battle ensued between the disorganized Ming army and the vanguard of the Mongol army, with Esen himself choosing not to participate. Only 20,000 Mongols were involved in the battle but the hungry and thirsty Ming soldiers were unable to put up much resistance. The Ming army suffered a swift defeat, with nearly half of its soldiers lost and a significant amount of weapons and equipment seized by the Mongols.

Among the casualties were high-ranking officials, including two dukes, two marquises, five counts, several generals, and hundreds of officials. Notable figures such as the old general Zhang Fu and the grand secretaries Cao Nai and Zhang Yi were also killed. After reclaiming the area, Ming troops were able to gather tens of thousands of firearms, armor, and other equipment left behind by the defeated army.

Enthronement of a new emperor and the defense of Beijing

On 15 September, officials in Beijing urged the Prince of Cheng to assume the role of emperor to stabilize the government and reduce the importance of the captured Emperor Yingzong in the hands of the Oirats. Although initially hesitant, the prince eventually ascended the throne as the Jingtai Emperor on 17 (or 23) September. He declared his captive brother as the "emperor emeritus" (Taishang Huangdi), a title that was purely honorary.