Why did cooperation among the Mongol khanates weaken over time?

Cooperation among the Mongol khanates weakened over time due to a combination of structural, cultural, and political factors that undermined the unity of the Mongol empire.

• Decentralization and Succession: The empire was initially divided into ulus (territories) among Genghis Khan’s sons, which fostered independence rather than cohesion. Frequent disputes over the succession of the great khan created deep-seated rivalries between different branches of the imperial family, such as the houses of Ögödei, Chagatai, and Tolui.1234
• Cultural Assimilation: As the khanates settled into diverse regions, they adopted the local cultures and religions of their subjects. The Golden Horde became Turkic and Muslim, the Il-Khans adopted Persian and Islamic traditions, and the rulers in China became Sinicized. This cultural divergence made the disparate parts of the empire increasingly alien to one another.32
• Economic and Military Shifts: The end of rapid expansion reduced the military incentives for unity, as promotion and spoils became scarcer. Additionally, the khanates began to pursue independent economic interests, and the devastating impact of the Black Death further disrupted trade and imperial authority.35

Ultimately, these factors led the successor states to prioritize their own regional autonomy, effectively ending the period of relative stability known as the Pax Mongolica.35