Zhengtong Emperor
Despite withdrawal from the steppe, the Ming military remained in a strong position until the Tumu Crisis in 1449, which caused the collapse of the early Ming security system. Over half of the campaigning Chinese army perished in the conflict, while the Mongols captured the Zhengtong Emperor. This military debacle shattered the Chinese military might that had so impressed and given pause to the Mongols since the beginning of the dynasty, and the Ming were on the defensive from this point on.