Tumu Crisis The Tumu Crisis ( ) ( ) ; also called the Crisis of Tumu Fortress ( ) or Battle of Tumu ( ) , was a frontier conflict between the Oirat Mongols and the Chinese Ming Dynasty which led to the capture of the Zhengtong Emperor on September 1 , 1449 , and the defeat of an army of 500 , 000 men by a much smaller force . 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 . This battle was also the very early decline in the Ming Dynasty . In July 1449 Esen Tayisi ( Chinese : 也先台吉 ) of the Oirat Mongols launched a large - scale , three - pronged invasion of China with his puppet khagan Toqtaq - Buqa . He personally advanced on Datong ( in northern Shanxi province ) in August . The eunuch official Wang Zhen , who dominated the Ming court , encouraged the 22 - year - old Zhengtong Emperor to lead his own armies into battle against Esen . The size of Esen ' s army is unknown but a best guess puts it at some 20 , 000 men . The Ming army of about 500 , 000 was hastily assembled ; its command was made up of 20 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 a 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 wanted to halt and send the emperor back to Beijing , but their opinions were overruled by Wang Zhen . 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 back toward China proper . Fearing that the restless soldiers would cause damage to his estates in Yuzhou , Wang Zhen decided 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 Gen . 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 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 . A battle ensued between the disorganized Chinese army and the advance guard of Esen ' s army ( Esen was not at the battle ) . The Chinese army basically dissolved and was almost annihilated . The Mongols captured a huge quantity of arms and armour while killing most of the Chinese troops . 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 he was sent to Esen ' s main camp near Xianfu . The entire expedition had been unnecessary , ill - conceived and poorly commanded . The Mongol victory was won by an advance guard of perhaps as few as 5 , 000 cavalry . Esen , for his part , was not prepared for the scale of his victory or for the capture of the Ming Emperor . At first he attempted to use the captured emperor to raise a ransom and planned to conquer the undefended Ming capital of Beijing . However , his plan was foiled due to the steadfast leadership of the Ming commander in the capital , Gen . Yu Qian . The Ming leaders rejected Esen ' s offer , Yu stating that the country was more important than an emperor ' s life . The Ming never paid a ransom for the return of the Emperor , and Esen released him four years later . Esen himself faced growing criticism for his failure to exploit his victory over the Ming and he was assassinated six years after the battle in 1455 . Although the Oirats later occupied the Ordos Desert , they never again seriously threatened the Ming state . See also . Battle of the Badger Mouth Battle of Mohi Battle of Legnica List of battles by casualties