Transylvania (Hungarian Erdely and German Siebenburgen) located in today’s Romania northern from the Carpathian Mountains was conquered by the Hungarians about year 900. A short period of independence at the beginning of the 11th century was followed by incorporation of Transylvania into the Kingdom of Hungary as an autonomous vassal duchy ruled by a prince or voivod responsible to the Hungarian King. Transylvania was settled by the German Saxons who were invited by the Hungarian King Geza II in the 12th and 13th century. The Saxons, the Szeklers (a Hungarian-speaking community of unknown origin) and Hungarian nobility formed the Union of the Three Nations as a ruling social class in Transylvania. The Romanian population mostly belonged to the class of serfs and was excluded from the political life.
Like the Balkan Peninsula, Transylvania was faced with the Ottoman threat at the end of the 14th century. The leader of the resistance against the Ottomans became John Hunyadi who was rewarded with the captaincy of the fortress of Belgrade and the governorship (voivodship) of Transylvania in 1440 for his support to the candidacy of Ladislaus III of Poland to the Hungarian throne. He decisively defeated the Ottoman forces at the Siege of Belgrade in 1456 and repulsed the Ottoman threat to southern Hungary for the next seven decades. John Hunyadi died of plague three weeks after the lifting of the Siege of Belgrade, while his younger son Matthias Corvinus (1458-1490) succeeded Ladislaus the Posthumous as King of Hungary in 1458.