To the east of the Danube, the Great Hungarian Plain (Hung. Alföld) extends beyond the Hungarian boundaries to the Carpathians and the Transylvanian Alps. The Dráva and Tisza rivers are also important waterways. To the west of the Danube is the Little Alföld and the Transdanubian region, which are separated by the Bakony and Vértes mts. The Mátra Mts. in the north reach a height of 3,330 ft (1,015 m) at Kékes, the highest peak in Hungary. Lake Balaton, the largest lake in Hungary and in central Europe, is a leading resort area. Hungary has cold winters and hot summers; springs and autumns are short. Situated on a plain near the geographic center of Europe, Hungary has been the meeting place and battleground of many peoples, and its heterogeneous population was often the cause of social upheaval before 1919. However, as a result of the separation of non-Hungarian territories after World War I, the great slaughter of the Jews in World War II, and the exchange after the war of Slavic and Romanian minorities for their Magyar counterparts, Hungary is today essentially homogeneous. The Magyars constitute about 90% of the population. There are small minorities of Gypsies, Germans, Serbs, and other groups. Hungarian is the official language. About two thirds of the people are Roman Catholic, but there is a large Calvinist minority. Hungary still has the largest Jewish population in Central and Eastern Europe (100,000-120,000).