The Slavs arrived in the territory of present day Slovakia in the fifth and sixth 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 United States of Greater Austria.