Esen Taishi

Esen rain into conflict with the Ming dynasty (明朝). The Ming Dynasty had for some time pursued a "divide and rule" strategy in dealings with their northern neighbors, maintaining trade relationships, functioning as a kind of state-subsidized monopoly, with multiple leaders who they could then turn against one another by inciting jealousy or suggesting intrigue. However, a unified Northern Yuan was less susceptible to such tactics. Many of the tribes brought under Oirat dominion had inhabited areas claimed by the Ming, and other tribes had been pushed south into Ming territory seeking to escape Oirat subjugation. The Chagatayid Hami oasis, furthermore, had paid tribute to the emperor before Esen convinced its ruler to pay tribute to the Oirats instead. Throughout the 1440s, Esen increased both the frequency of tribute missions to the Ming and the number of representatives sent on each mission. According to surviving Chinese accounts, the Oirats asked for more and more lucrative tribute and trade agreements.

The Ming tried to stir rivalry between Taisun Khan, but Esen chose "rivals" below him in status to counter the divide and rule strategy. So the Ming resorted to another strategy: to buy off the Northern Yuan with gifts.

Esen encouraged hundreds of Mongol, Hami, and Samarkand-based Muslim merchants to accompany his missions to the Ming Emperor. Beginning in 1439 Taisun Khan and Esen sent envoys to the Ming, often numbering more than 1,000. They asked for more and more gifts. In response to this inflation of numbers, the Zhengtong Emperor (1427–64; 大明英宗正統皇帝；明英宗) decreased trade with Esen and Taisun Khan, and closed border trade with the Northern Yuan.

In retaliation to these trade sanctions, Esen Taishi led an invasion of the northern Ming in 1449 that culminated in the capture of the Ming emperor during the Tumu Crisis (土木之變). The large-scale, three-pronged invasion began in July, with Taisun Khan leading the easternmost force to Liaodong, the grand councillor Alag attacking Xuanfu, and Esen himself leading the troops that sacked Datong in August. Another column of the Mongols invaded Ganzhou.

The campaign was a massive victory for the Northern Yuan, with the Mongols crushing Zhu Qizhen's forces. Even though Zhu's troops in the region are estimated to have numbered as many as 500,000, Zhu was still crushed by Esen Taishi's 20,000 cavalry. Datong lay next to the south side of the Great Wall of China. After the initial attack on Datong, Esen pretended to retreat back into the Mongolian steppes. The emperor and his hastily raised army chased the invaders west and met an ambush upon arriving at Datong. Mongol horsemen harried Zhu's retreat back towards the wall for four days while hampered by thunderstorms. The imperial army eventually reached the Tumu Fortress. However rather than having secured a defensible position, Zhu's troops were trapped against the northern side of the fortress, and the Northern Yuan horsemen annihilated Zhu's army.

Zhu Qizhan, captured by Esen Taishi

Most of the remaining soldiers were slaughtered. Esen was still some distance away, near Xianfu. Six weeks later, when the captured emperor Zhu Qizhen was brought to his camp, Esen attempted to ransom the emperor back to the Ming. According to some accounts, it was at this point that Esen was granted the title "Taishi."

In any case, the Ming refused to negotiate a ransom, perhaps in part because the emperor's brother (prince Zhu Qiyu, later the Jingtai Emperor) was by then installed on the throne and not eager to give up his new position. Yu Qian (于謙), the defense minister of Ming, who was organizing the counterstrike, commented that the emperor's life is not as important as the fate of the country. He also believed that ransoming the emperor might boost the Northern Yuan's morale and reduce that of the Ming.

Esen still considered the emperor more valuable alive than dead. Esen then laid siege to Beijing, but it failed.

Esen offered the emperor his sister in marriage (Heqin), but the emperor rejected Esen. The Ming Beijing garrison led by Yu Qian soon turned the situation around. Yu Qian ordered his forces to pretend that they had lost control of the city gate in order to lure Mongol horsemen into the city. Once a large portion of the Mongol force was inside, the gate was shut and the Mongols were ambushed. Esen's sworn blood brother was killed in the attack. Having failed to take the city, Esen was forced to retreat under pressure from his own troops and by the arrival of Ming reinforcements.

Esen and Taisun Khan turned to attack Manchuria and East Siberia, under Ming rule, around the Nen River and Songhua River, but failed and were defeated by the Ming.

The Ming court elevated the Jingtai Emperor (reigned 1449–57) to the throne. Esen sent the captured emperor back in 1450. Since the Mongol economy relied on their trade with Ming China, Esen was obligated to reopen negotiations, now under a much weaker position. While Ming-Mongol trade did not cease entirely during the Tumu Crisis, Esen had not only failed to win better terms than the prior arrangements, he was forced to accept less favorable terms in return for resumption of trade with the Ming. The North Yuan then entered a vassal relationship with the Ming for some time.

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