China, at the outbreak of war, was effectively controlled (in large part) by five greet powers, Britain, France, Russia, Germany and Japan, through what was known as spheres of influence.  Within these spheres the respective nations held sway, and even the Chinese government could not enforce its own laws if push came to shove.

This map shows the situation at the end of the Qing Dynasty (1911). Mongolia was part of China at that time.