Wasn't Transylvania (as well as a few odd other princedoms around there) for all intents and purposes independent entities for most of the Middle Ages and the Early Modern period ? You see references to them as independent actors in quite a few writings on the Ottoman-everyone conflicts in the region...
But then, feudal barons were often beholden to their nominal superiors in pure theory only and the Balkans-Central Europe region doesn't appear to have ever been very conductive to close control from power centers outside it. Probably all those mountains that did it. Nobody was ever too good at ruling the high ground.
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