The Fractured Mongol World After the Yuan Dynasty

The early 15th century witnessed a dramatic power shift in the Mongolian steppe as the Oirats (瓦剌), a western Mongol faction, rose to challenge the dominant Eastern Mongols (鞑靼). This transition occurred against the backdrop of a fragmented post-Yuan political landscape, where various Mongol groups vied for supremacy while maintaining complex relationships with the Ming Dynasty.

Following the collapse of the Yuan Dynasty in 1368, the Mongols retreated to their northern homeland but never abandoned hopes of reconquest. The Great Khan’s authority had weakened significantly, creating opportunities for ambitious leaders from non-Chinggisid lineages to assert power. The Oirats, originally forest-dwelling people from the Altai region, had gradually transformed into formidable steppe warriors through their interactions with other Mongol groups.

The Tumultuous Rise of the Oirats Under Toghon

The Oirats’ path to dominance began under the leadership of Mahamud (马哈木), who suffered significant defeats against the Eastern Mongols and died around 1416, leaving his son Toghon (脱欢) with a weakened faction. Toghon’s subsequent consolidation of power marked a turning point in Mongol politics.

Through ruthless internal struggles, Toghon eliminated rival leaders including Taiping (太平) and Batu Bolod (把秃孛罗), absorbing their forces. What made Toghon particularly remarkable was his rejection of traditional Chinggisid legitimacy – the belief that only descendants of Genghis Khan could claim the title of Great Khan. The “Golden Chronicle” (黄金史纲) records a striking legend where Toghon allegedly challenged Genghis Khan’s spirit in the sacred “Eight White Tents” (八白帐), declaring his right to rule based on his maternal lineage from Chinggisid princesses.

Toghon’s political maneuvers demonstrated how decades of feudal warfare had eroded traditional Mongol political norms. He skillfully employed a “befriend the distant while attacking the near” strategy, maintaining tributary relations with the Ming Dynasty while aggressively expanding eastward against the Eastern Mongols.

The Fall of the Eastern Mongols and Oirat Ascendancy

The Eastern Mongols, led by Arughtai (阿鲁台), found themselves trapped between Ming military campaigns and Oirat expansion. Emperor Yongle’s (永乐) repeated northern expeditions had already weakened Arughtai’s forces significantly. Following Yongle’s death in 1424, the Ming adopted a more passive stance, allowing Toghon to deliver the final blows.

By the Xuande era (1426-1435), the Oirats had seized the Eastern Mongols’ homeland. Arughtai fled westward with his remaining forces but was eventually killed in battle. His son Ajai (阿台汗), the last nominal Great Khan of the Eastern Mongols, became a wandering fugitive before being captured and executed by Toghon in 1438. Remarkably, both Toghon and Ajai died in the same year, marking the end of an era.

Esen Taishi’s Expansion and the Road to Tumu

Toghon’s son Esen Taishi (也先) inherited a powerful confederation and continued his father’s expansionist policies. He installed a Chinggisid puppet khan, Togtoh Bukha (脱脱不花), to legitimize his rule while consolidating control over key trade routes and Mongol groups from the Altai to Manchuria.

Esen’s growing power coincided with Ming military decline. The once-formidable Ming armies suffered from systemic problems: rampant desertion (totaling 1.6 million by 1449), corrupt officers embezzling military colony lands, and inadequate training. Ironically, Ming border officials even secretly traded weapons to the Oirats, including the eunuch Guo Jing (郭敬) who smuggled arrowheads hidden in jars.

The breakdown in Ming-Oirat relations came over trade disputes. Oirat tribute missions ballooned from 50 to 3,500 members, straining Ming resources. When the Ming reduced gifts in 1448, Esen used this as pretext for invasion. In July 1449, he launched a four-pronged attack, personally leading forces against Datong while sending others to Liaodong, Xuanfu, and Ganzhou.

The Tumu Crisis and Its Aftermath

The Ming response to Esen’s invasion proved disastrous. The young Emperor Zhengtong (正统), advised by the eunuch Wang Zhen (王振), personally led a hastily assembled army northward. Poorly supplied and commanded, the Ming forces were outmaneuvered by Oirat cavalry. At Tumu Fortress (土木堡) in September, surrounded without water and attacked by Oirat heavy cavalry, the Ming army was annihilated. The emperor himself was captured – an unprecedented humiliation.

Esen’s subsequent attempt to besiege Beijing in October failed against the determined defense organized by Yu Qian (于谦). The Ming regrouped, declared a new emperor (景泰), and repelled the Oirats using combined arms tactics that emphasized city defense and coordinated infantry-cavalry operations.

Legacy of the Oirat Ascendancy

The Oirat-Ming conflicts had profound consequences. For the Mongols, the Oirat ascendancy demonstrated that non-Chinggisids could achieve supreme power, though Esen’s eventual assassination in 1454 showed the limits of this transformation. The Ming, traumatized by Tumu, became increasingly defensive, focusing on fortifications like the Great Wall rather than steppe expeditions.

The events also revealed structural weaknesses in both societies. The Ming military system never fully recovered from its mid-15th century crisis, while Mongol unity proved fleeting without strong leadership. Yet the period also saw important military innovations, particularly Yu Qian’s “regimental camps” (团营) that combined firearms with traditional infantry tactics.

Ultimately, the Oirat interlude represents a crucial transitional period in Inner Asian history, when old certainties about political legitimacy were challenged, and new patterns of Ming-Mongol relations emerged that would shape East Asian geopolitics for centuries to come.