The Tumu Crisis (Chinese: 土木之變; pinyin: Tŭmù zhī bìan); also called Crisis of Tumubao (土木堡之變); or Battle of Tumu (土木之役), was a frontier conflict between Mongolia and the Chinese Ming Dynasty which led to the capture of the Zhengtong Emperor on September 8, 1449. This outcome was largely due to the Chinese army's remarkably bad deployment. The Ming expedition is regarded as the greatest military debacle of the dynasty.
In July 1449 Esen Tayisi (也先) of the Oirat Mongols launched a large-scale three-pronged invasion of China. He personally advanced on Datong (in northern Shanxi province) in August. The eunuch official Wang Zhen, who dominated the Ming court, encouraged the twenty-two year old Zhengtong Emperor to lead his own armies into battle against Esen (20,000 derbet cavalry). A huge army (perhaps as many as 500,000 men) was hastily assembled. Its command was made up of twenty experienced generals and a large entourage of high-ranking civil officials, with Wang Zhen acting as field marshal.
On August 3, Esen's army crushed a badly supplied Chinese army at Yanghe, just inside the Great Wall. The same day the Emperor appointed his half-brother Zhu Qiyu as regent. The next day he left Beijing for Juyong Pass. The objective was a short, sharp march west to Datong via the Xuanfu garrison, a campaign into the steppe, and then to return to Beijing by a southerly route through Yuzhou.
Initially the march was mired by heavy rain. At Juyong Pass, the civil officials and generals wished to halt and send the emperor back to Beijing, but their opinions were overruled by Wang Zhen. On August 12, some of the courtiers discussed assassinating Wang. On August 16, the army came upon the corpse-strewn battlefield of Yanghe. When it reached Datong on August 18, reports from garrison commanders persuaded Wang Zhen that a campaign into the steppe would be too dangerous. The "expedition" was declared to have reached a victorious conclusion and on August 20 the army set out toward Beijing.
Fearing that the restless soldiers would cause damages to his estates in Yuzhou, Wang Zhen took the decision to strike northeast and return by the same exposed route as they had come. The army reached Xianfu on August 27. On August 30, the Mongols attacked the rearguard east of Xianfu and wiped it out. Soon afterwards, they also annihilated a powerful new rearguard of cavalry led by the elderly general Zhu Yong at Yaoerling. On August 31 the imperial army camped at the post station of Tumu. Wang Zhen refused his ministers' suggestion to have the emperor take refuge in the walled city of Huailai, just 45 km ahead.
Esen sent an advance force to cut off access to water from a river south of the Chinese camp. By the morning of September 1, they had surrounded the Chinese army. Wang Zhen rejected any offers to negotiate and ordered the confused army to move toward the river. The Mongols attacked in force and destroyed the Chinese army, capturing large quantities of arms and armour. All the high-ranking Chinese generals and court officials were killed. According to some accounts, Wang Zhen was killed by his own officers. The emperor was captured, and on September 3 was sent to Esen's main camp near Xianfu.
The entire expedition had been unnecessary, ill-conceived, and ill-prepared. The Mongol victory was won by an advance guard of only 20,000 cavalry. Esen, for his part, was quite unprepared either for the scale of his victory or for the capture of the Ming emperor.
At first, Esen attempted to use the captured emperor to raise a ransom and planned to conquer the undefended Beijing. However his plan was foiled, due to the brilliant Ming commander, Yu Qian who rejected his offer, since Yu stated the country was more important than an emperor's life and through a battle near Beijing, Yue have successfully eliminated the proud Mongolian Army. Esen never recovered his glory afterward and his assassination soon followed.