Slovak Republic (or, in short form, Slovakia ; Slovak: Slovensko, long form Slovenská republika ) is a landlocked state in Central Europe. It has a population of over five million and an area of about 49,000 square kilometres (19,000 sq mi). Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south. The largest city is the capital, Bratislava, and the second largest is Košice. Slovakia is a member state of the European Union, NATO, United Nations, OECD and WTO among others. The official language is Slovak, a member of the Slavic language family. The Slavs arrived in the territory of present-day Slovakia in the 5th and 6th centuries during the migration period. In the course of history, various parts of today's Slovakia belonged to Samo's Empire (the first known political unit of Slavs), Principality of Nitra (as independent polity, as part of Great Moravia and as part of Hungarian Kingdom), Great Moravia, Kingdom of Hungary, the Austro-Hungarian Empire or Habsburg Empire, and Czechoslovakia. A separate Slovak state briefly existed during World War II, during which Slovakia was a dependency of Nazi Germany between 1939 and 1944. From 1945 Slovakia once again became a part of Czechoslovakia. The present-day Slovakia became an independent state on 1 January 1993 after the peaceful dissolution of Czechoslovakia.