At the age of 21, in 1449, the Zhengtong Emperor, advised by Wang Zhen, personally directed and lost the Battle of Tumu Fortress against the Mongols under Esen Taishi (d.1455).
Although the Zhengtong Emperor was a prisoner of the Mongols, he became a good friend to both Tayisung Khan Toghtoa Bukha (1416-1453) and his grand preceptor (taishi) Esen.