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
Transylvania 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. It is a subject of dispute whether elements of the mixed Daco–Roman population survived in Transylvania through the Post-classical Era (becoming the ancestors of modern Romanians) or the first Vlachs/Romanians appeared in the area in the 13th century after a northward migration from the Balkan Peninsula. There is an ongoing scholarly debate over the ethnicity of Transylvania's population before the Hungarian conquest (see Origin of