Protectorate

noun

1. Government by a protector; especially, the government of England, Scotland, and Ireland by Oliver Cromwell.
2. The authority assumed by a superior power over an inferior or a dependent one, whereby the former protects the latter from invasion and shares in the management of its affairs but the protected state retains its nominal sovereignty.

   "Egypt became a British protectorate in 1914."

3. An autonomous territory that is protected diplomatically or militarily against third parties by a stronger state or entity.