China had to define its relations with Bhutan for the first time around 1910. This was necessitated by the Treaty of Punakha, signed on 8 January of that year, between Bhutan and British India, in the context of their shared threat perception from China. In the absence of either formal treaty relations or traditional "patron-priest" relations, China defined relations in the context of the "tributary system." However, Bhutan had never been a vassal state of imperial China. (History & Geopolitical)