Initially, he attempted to use the captured emperor to raise a ransom and planned to conquer the undefended Ming capital of Beijing.

Hereditary soldiers from Weisuo garrisons were often exploited by officers, leading to a reliance on inadequate grain supplies from the interior.

[6] The defense of the northern border was primarily focused on the area between China and the steppe, as the outposts in present-day Inner Mongolia had been abandoned.

[9] The border patrol battalions were meant to hold off the enemy until the main forces arrived, but with Xuanfu only 180 km from Beijing, the defense system lacked depth[9] and relied on a quick and decisive response to any attack.

Their chief, Toghon, the Choros taishi, or "grand marshal", strengthened their authority by arranging for his daughter to marry the young khan of the Eastern Mongols, Toghtoa Bukha.

[13] Esen was more ambitious than his father, and in 1443 and 1445, he launched attacks on Hami, an important city on the route from China to Central Asia near the Chinese border.

[12] In Beijing, he was viewed as a threat by those who opposed Wang Zhen, a powerful eunuch who held great influence at the imperial court in the 1440s.

[6][d] In their relationship with China, the Mongols were primarily interested in free trade, specifically in the exchange of horses for tea, silk, and other luxury goods.

However, the Ming government imposed restrictions and regulations on trade, limiting it to a few designated border towns, with Datong being the main hub.

[12] As a result, the Ming government protested against the excessive number of incoming Mongols, causing a sharp deterioration in their relationship.

[10] The main objective of this campaign was to capture the fortified cities of Xuanfu and Datong, which would grant the Mongols unrestricted access to the northern regions of China.

[19] On the same day, Emperor Yingzong appointed his younger brother Zhu Qiyu, Prince of Cheng, to oversee the administration of the capital during the campaign.

These included Prince Consort Commander Jiao Jing (焦敬), who represented the imperial family; Jin Ying, the head of the Directorate of Ceremonial and the highest-ranking eunuch in the absence of Wang Zhen; Minister Wang Zhi, who led the government; and Grand Secretary Gao Gu (高穀).

[18] The emperor was accompanied by twenty experienced generals, most of whom held noble titles, and an equal number of high-ranking officials.

[21] By 12 August, some officials were already discussing the possibility of assassinating Wang Zhen and bringing the emperor back, but they lacked the courage to follow through with their plan.

[21] Upon reaching Datong, Wang Zhen received reports from local commanders and information from nearby border garrisons, which convinced him that continuing the campaign into the steppe would be dangerous.

Wang Zhen was also concerned about the impact of the army's passage on his hometown in Yuzhou (present-day Yu County, Hebei), so he insisted on returning the same way they had come.

The Mongols then proceeded to Yao'er Gorge, where they ambushed and destroyed a newly formed rear guard of 40,000 cavalry under the command of General Zhu Yong (朱勇).

Despite suggestions from ministers, Wang Zhen refused to seek refuge in the nearby walled city of Huailai, which was only 10.5 km away.

[21] The Ming army suffered a swift defeat, with nearly half of its soldiers lost and a significant amount of weapons and equipment seized by the Mongols.

[23] After reclaiming the area, Ming troops were able to gather tens of thousands of firearms, armor, and other equipment left behind by the defeated army.

[1] Reader-in-waiting Xu Cheng,[1][g] a native of Suzhou known for his military strategy skills and familiarity with the border situation, suggested temporarily moving the capital to the south to keep it safe from the enemy.

Minister of Rites Hu Ying opposed this plan, arguing that the tombs of the Yongle and Xuande emperors could not be abandoned.

[i] This calmed down the panicking officials, as Yu Qian was supported by influential eunuchs and Grand Secretaries Chen Xun (陳循) and Shang Lu (商輅).

Although Empress Dowager Sun reluctantly approved staying and authorized any necessary actions to defend the capital, many officials chose to flee south, and some sent their families there for safety.

[26] Additionally, she also promoted the two-year-old Zhu Jianshen,[21] eldest son of the captured emperor, to the position of crown prince.

[j] The Prince of Cheng also supported Yu's plan to gather military units from nearby provinces and the south, as well as levies from the metropolitan area.

[21] In response to the threat of invasion from the Mongols, Yu Qian withdrew 80,000 soldiers from Xuanfu and other areas to defend Beijing.

Following Esen's failed campaign, the Ming troops were able to drive out the remaining smaller Mongol forces from China.

[33] Although the initial impact of losing the battle and capturing the emperor was significant, the fortified cities were able to hold their ground against the Mongols, preventing them from permanently occupying any territory.