noun
vassal state; dependency
A state that is subordinate to a more powerful state, often in a historical or political context.
その小国は長い間、隣の大国の属国だった。
That small country was a vassal state of the neighboring great power for a long time.
歴史的に、多くの属国が宗主国に貢物
Historically, many vassal states paid tribute to their suzerain.
Compound of 属 (zoku, 'belong to, subordinate') and 国 (koku, 'country'). The reading ぞっこく is a regular on'yomi combination.