Transylvania as originally defined in Treaty of Trianon, 27 years earlier, thus confirming the return of Northern Transylvania to Romania. From 1947 to 1989, Transylvania, along with the rest of Romania, was under a communist regime. The ethnic clashes of Târgu Mureș occurred between ethnic Romanians and Hungarians in March 1990 after the fall of the communist regime and became most notable inter-ethnic incident in the post-communist era. The Transylvanian Plateau, high, is drained by the Mureș, Someș, Criș, and Olt rivers, as well as other tributaries of the Danube. This core of historical Transylvania roughly corresponds with nine counties of
Northern Transylvania After the Roman legions withdrew in 271 AD, it was overrun by a succession of various tribes, bringing it under the control of the Carpi, Visigoths, Huns, Gepids, Avars and Slavs. From 9th to 11th century Bulgarians ruled Transylvania. The Magyars conquered much of Central Europe at the end of the 9th century and for almost six hundred years, Transylvania had been a voivodeship in the Kingdom of Hungary. After the Battle of Mohács in 1526, and the Hungarian defeat by the Ottomans, Transylvania became a semi-independent principality (Principality of Transylvania) under native Hungarian rule but owing suzerainty to the