Transylvania is presented in Romanian historiography in parallel with the other two "Principalities" with which it ended up united in the 20th century - Wallachia and Moldavia. These two had been under Hungarian suzerainty at some point, and the king of Hungary was instrumental in the creation of at least one of them during his fight against the Golden Horde (namely Moldavia).
Both of these two Romanian-speaking states later enjoyed a relative autonomy by balancing allegiances between Hungary, Poland and the Ottomans. Their integration within the European feudal order was problematic, given their non-Catholic Christianity, and their rulers were considered only as "princes", not as kings, although this may have derived more from their heterogeneity rather than their vassal status in relation to a king.
The autonomous principality of Transylvania is a later phenomenon, but when it happened, this statehood had a lot of the characteristics mentioned above with respect to the other two principalities: only relative autonomy (but some poignant action at times, such as taking part to the 30 Years' War in the Protestant camp), only principality and not kingdom, balance between foreign powers, and frequent switching of allegiances.
I suspect nationalist discourse and a projection of the present into the past play a great role in Romanian historiography as far as the similitude between Wallachian/Romanian (future Danubian) Principalities and the Principality of Transylvania is concerned. But at the same time I cannot help but wonder: Is there nothing more than that?
Hungary (along with Poland and other Eastern powers - see the link above) differs in its feudal order and kingship from the Carolingian area.
Transylvania was one of the lands of the Hungarian crown. It became separate after the partitioning of the kingdom as a result the defeat at Mohács by the Ottomans on 29 August 1526. The Turkish occupation of Hungary-proper created the conditions for autonomy, confirmed by the Treaty of Speyer (1570).
And so, the Principality of Transylvania existed as a semi-independent state, ruled primarily by Hungarian princes, between 1570 and 1711, when the princes of Transylvania were replaced with Habsburg governors. But were there any such princes before that? How did the King of Hungary administer this territory before the catastrophic defeat against the Turks? Was it a appanage of the king? Was it that of a prince, duke or other lord?
Was there any tradition of autonomy of Transylvania within the Kingdom of Hungary before 1525-1570?