From Wiktionary, the free dictionary
vassal state (plural vassal states)
- A state that is subordinate to another; government chiefly directed by the interests of an overlord or patron state.
- Coordinate term: satellite state
2023 June 22, Valerie Hopkins, quoting Emmanuel Macron, “Belarus Is Fast Becoming a ‘Vassal State’ of Russia”, in The New York Times[1], →ISSN:At a recent conference in Slovakia, President Emmanuel Macron of France called Belarus a “vassal state,” but said Europe bore some of the blame.
state that is subordinate to another