The Oirat leader Esen Tayisi 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 Qiyu 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 "Wresting the Gate Incident". The former emperor retook the throne under the new era name Tianshun (r. 1457–64).