Why did Mongolia have autonomy under Chinese suzerainty after 1915?

Following the 1911 Chinese Revolution, Mongolia declared its independence from Manchu rule. However, this status was contested by international powers. While the Bogd Khan’s government viewed the country as independent, Russia characterized Mongolia as "autonomous" to balance its own diplomatic interests.

This position was formalized in a 1913 declaration between Russia and China, which asserted that Mongolia remained under Chinese suzerainty. This status was ultimately codified in the 1915 tripartite treaty between Russia, China, and Mongolia. Under the terms of this agreement, the Bogd Khan’s government was compelled to accept autonomy under Chinese suzerainty, effectively preventing the unification of Inner and Outer Mongolia and limiting the region's sovereignty.12