Editing Tumu Crisis (section)

===Sino–Mongol relations===
The Mongols were divided into three groups: the [[Uriankhai]] in the southeast, the [[Tatar (Mongolia)|Eastern Mongols]] (also known as Tatars) in the east, and the [[Oirats]] in the west.{{sfnp|Twitchett|Grimm|1988|p=316}} After [[Arughtai]], leader of the Eastern Mongols, was defeated in 1434, the Oirats took control over [[Mongolian Plateau]]. Their chief, Toghon, the [[Choros (Oirats)|Choros]] taishi, or "grand marshal", strengthened their authority by arranging for his daughter to marry the young khan of the Eastern Mongols, [[Taisun Khan|Toghtoa Bukha]].{{efn|A puppet khan installed by Toghon in 1439. Toghon was not a descendant of Genghis and therefore could not become a khan, even though he effectively ruled over Mongolia.{{sfnp|Twitchett|Grimm|1988|p=317}}{{sfnp|de Heer|1986|p=13}}}} After Toghon's death in 1440, his son [[Esen Taishi|Esen]] inherited the title of taishi, and "de facto ruler of all Mongols".{{sfnp|de Heer|1986|p=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. In 1448, he successfully conquered it. He also attempted to gain the support of the Mongol divisions in the Ming army in the western Chinese province of [[Gansu]]. In the east, his authority extended to the borders of Korea.{{sfnp|Twitchett|Grimm|1988|p=317}} In Beijing, he was viewed as a threat by those who opposed [[Wang Zhen (eunuch)|Wang Zhen]], a powerful eunuch who held great influence at the imperial court in the 1440s.{{sfnp|de Heer|1986|p=14}}{{efn|Wang Zhen profited from illegal trade activities, such as selling metal tools and weapons to the Oirats. As a result, he ignored proposals to strengthen defenses on the northern border and warnings about threats from Esen.{{sfnp|de Heer|1986|p=15}}}}

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.{{sfnp|Twitchett|Grimm|1988|p=317}} As Esen's power and influence expanded, so did his dependence on these goods to maintain the loyalty of the Mongol tribes.{{sfnp|de Heer|1986|p=15}} This led to a significant number of Mongols in border markets in the late 1440s, with up to two thousand arriving each year.{{sfnp|Twitchett|Grimm|1988|p=317}} The large number of armed horsemen posed a serious security concern for the Ming authorities.{{sfnp|Twitchett|Grimm|1988|p=317}} As a result, the Ming government protested against the excessive number of incoming Mongols, causing a sharp deterioration in their relationship. In 1449, the Ming ultimately rejected the Mongols' request for goods and only provided them with a fifth of what was requested. This rejection led the Mongols to resort to force. The immediate cause of the war was Ming's refusal to grant Esen's request to marry an imperial princess for his son.{{sfnp|de Heer|1986|p=15}}