How was the Mongol empire divided among Genghis Khan’s sons after his death?

Genghis Khan divided his empire among his four sons, each receiving a vassal kingdom known as an ulus—a term denoting supremacy over specific tribes rather than strictly defined borders. This division followed nomadic traditions where sons were granted shares of the inheritance as they reached manhood, with the youngest son remaining as the "guardian of the hearth and fire" to receive the residual heritage.12

The distribution was as follows:

• Jöchi (eldest): Received the western lands stretching from the Yenisey River and the Aral Sea as far west as Mongol horses could reach, an area that later formed the Golden Horde.12
• Chagatai: Received the lands of Khara-Khitai, including Kashgaria and most of Mavrannakhar between the Amu Darya and Syr Darya.12
• Ögödei: Received western Mongolia and the Tarbagatai region (modern northwestern Xinjiang).12
• Tolui (youngest): Inherited the ancient Mongol homeland in eastern Mongolia and adjacent parts of northern China.12

While these divisions were intended to maintain family unity under a great khan (khagan), the empire eventually fragmented into independent khanates as the separate branches adopted the diverse cultures of their subject populations.13