 The Oirat leader Esen <unk> launched an invasion into Ming China in July 1449 . The chief eunuch Wang Zhen encouraged the Zhengtong Emperor ( r . 1435 – 49 ) to lead a force personally to face the Oirats after a recent Ming defeat ; the emperor left the capital and put his half @-@ brother Zhu <unk> in charge of affairs as temporary regent . On 8 September , Esen routed Zhengtong 's army , and Zhengtong was captured — an event known as the Tumu Crisis . The Oirats held the Zhengtong Emperor for ransom . However , this scheme was foiled once the emperor 's younger brother assumed the throne under the era name Jingtai ( r . 1449 – 57 ) ; the Oirats were also repelled once the Jingtai Emperor 's confidant and defense minister Yu Qian ( 1398 – 1457 ) gained control of the Ming armed forces . Holding the Zhengtong Emperor in captivity was a useless bargaining chip for the Oirats as long as another sat on his throne , so they released him back into Ming China . The former emperor was placed under house arrest in the palace until the coup against the Jingtai Emperor in 1457 known as the " <unk> the Gate Incident " . The former emperor retook the throne under the new era name Tianshun ( r . 1457 – 64 ) . 
