Client kingdoms in ancient Rome
A client kingdom or people in ancient Rome meant a kingdom or ancient people that was in the condition of "appearing" still independent, but in the "sphere of influence" and thus dependence of the neighboring Roman Empire. It was a form of modern protectorate, where the kingdom or territory in question were controlled or occupied (under the guise of protection) by a stronger power.
Source: Wikipedia — Client kingdoms in ancient Rome (CC BY-SA 4.0)