The word of the day is suzerain:
< French suzerain, older s(o)userain , apparently < sus above, up ( < Latin sūsum , sursum , < sub from below, up + vorsum , versum , past participle of vertĕre to turn), after souverain sovereign n. and adj.
A feudal overlord. In recent use, with reference to international
relations, a sovereign or a state having supremacy over another state
which possesses its own ruler or government but cannot act as an
independent power. (OED)
"Sudan - derived from the Arabic word for 'land of the blacks' - was a lucrative source of chattel until the British suppressed the trade; the capital, Khartoum, in the north, was built by an Egyptian suzerain as a slaver station."
- Jon Lee Anderson, "A History of Violence", The New Yorker 23 July 2012