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A vassal state is any state that is subordinate to another. The vassal in these cases is the ruler, rather than the state itself. Being a vassal most commonly implies providing military assistance to the dominant state when requested to do so; it sometimes implies paying tribute, but a state which does so is better described as a tributary state. In simpler terms the vassal state would have to provide military power to the dominant state. Today, more common terms are puppet state, protectorate or associated state.
These ranged in size from small city states to vassals which controlled large swathes of territory such as the States of Chu and Qi. One of these vassal states would go on to conquer China and unite the country under the first emperor Qin Shi Huang.
The Ottoman Empire (1299–AD 1923 ) controlled a number of tributary or vassal states in the peripheral areas of its territory. Vassalage took a number of different forms with some states permitted to elect their own leaders. Other states paid tribute for their lands.