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 For most of this period, Transylvania, maintaining its internal autonomy, was under the suzerainty of the Ottoman Empire. The Habsburgs acquired the territory shortly after the Battle of Vienna in 1683. In 1687, the rulers of Transylvania recognized the suzerainty of the Habsburg emperor Leopold I, and the region was officially attached to the Habsburg Empire. The Habsburgs acknowledged Principality of Transylvania as one of the Lands of the Crown of Saint Stephen, but the territory of principality was administratively separated from Habsburg Hungary and subjected to the direct rule of the emperor's governors. In 1699 the Turks legally acknowledged