
The Khalkha and the Unification Efforts of Dayan Khan
By the late 15th century, the Khalkha Mongols emerged as a dominant force in Eastern Mongolia. Dayan Khan (1479–1543) undertook significant efforts to reunify the Mongols. With the support of his wife, Mandukhai the Wise, Dayan Khan defeated the Oirats and subdued rival factions within the right-wing tumens. He reorganized Mongolia into six tumens: three on the left wing (Khalkha, Chaharia, and Urianhai) and three on the right wing (Ordos/Tümed, Yunshiyebu, and Khorchin).
Dayan Khan's efforts stabilized the Mongol state and laid the groundwork for a period of relative unity. However, his successors struggled to maintain control, and power gradually shifted toward regional lords and autonomous khanates.

Location of the Four Oirats (Oirat confederation). © Khiruge
The Decline of Central Authority
By the late 16th century, the Northern Yuan dynasty had fragmented into a patchwork of semi-independent khanates. The descendants of Dayan Khan ruled over various territories in Northern Khalkha, while the Oirats established the Dzungar Khanate in Western Mongolia. In Southern Mongolia, Altan Khan’s successors continued to dominate the Tümed and Ordos regions.
The weakening of central authority left the Mongols vulnerable to external pressures. Economic hardships, exacerbated by Ming trade restrictions and frequent internal strife, further eroded their power. By the early 17th century, the Mongols faced growing challenges from both the rising Manchu state in the east and internal divisions, setting the stage for a new era of Mongolian history.