Despite his ambitions, Taisun Khan was still far more inclined towards peaceful relations with the Ming dynasty than his commander Esen. He kept a friendly relationship with the Ming court. His taishi, Esen, was even more ambitious and wanted to restore the glory of the
Mongol Empire in name and territory. Esen first directed his attention to the Hami Oasis where the Ming ally,
Borjigin prince descended from
Chagatai Khan, ruled. Repeated raids and threats by Esen forced him to surrender in 1448. Esen then attacked the
Gansu region where the Mongol satellite states of the Ming, known collectively as the Three Guards, were located. The Fuyu guard was forced to flee, and Esen appointed his own governor in the area. Taisun Khan personally led the attack on the Taining guard. After that, Esen also plundered the Doyin Uriankhai guard, forcing them to surrender. With the submission of the Three Guards, the revived Yuan dynasty became a direct threat to Ming. When the Ming refused the Mongols their request to allow additional Mongol envoys to China and a Chinese princess, Esen decided to invade the Ming. Taisun Khan was apprehensive of this and did not support Esen at first. However, he was induced to lead the easternmost force of Uriankhais to
Liaodong in 1449. He besieged the city and ravaged its outskirts for 40 days while Esen crushed the Ming armies en route to
Beijing. After defeating the Ming army during the
Tumu Crisis and capturing the
Zhengtong Emperor the Mongols returned north. Taisun Khan treated the captured emperor kindly. Upon realizing that the Ming would not pay a ransom for the captured emperor, the Zhengtong Emperor was returned in 1450. == Decline ==