dependency; vassal state; appanage
A political entity that is subordinate to a more powerful state, often in historical or geopolitical contexts. 'Appanage' is a rarer, more specific historical term.
That region was once a dependency of a great power.
歴史的に、多くの従属国が宗主国に貢物を納めていた。
Historically, many vassal states paid tribute to their suzerain.