suzerainty
A political term referring to the right of a dominant state (suzerain) to control the foreign relations of a vassal state while allowing it internal autonomy. Used mainly in historical and international relations contexts.
Suzerainty is a concept historically seen in the relationship between a protectorate and a suzerain state.
保護国 is a 'protectorate', the subordinate state in a suzerainty relationship. 宗主権 is the right or authority exercised by the suzerain.
Compound of 宗主 (suzerain) + 権 (right, authority). The term is a modern political concept, likely coined in the Meiji era to translate Western notions of suzerainty.