Poland (Polish: Polska [ˈpɔlska] ( listen)), officially the Republic of Poland (Polish: Rzeczpospolita Polska [ʐɛt͡ʂpɔˈspɔlita ˈpɔlska] ( listen)), is a country located in Central Europe. It is divided into 16 administrative subdivisions, covering an area of 312,679 square kilometres (120,726 sq mi), and has a largely temperate seasonal climate. With a population of approximately 38.5 millionpeople, Poland is the sixth most populous member state of the European Union. Poland's capital and largest metropolis is Warsaw. Other majorcities include Kraków, Łódź, Wrocław, Poznań, Gdańsk, and Szczecin.
The establishment of the Polish state can be traced back to A.D. 966, when Mieszko I, ruler of the realm coextensive with the territory of present-day Poland, converted to Christianity. The Kingdom of Poland was founded in 1025, and in 1569 it cemented its longstanding political association with the Grand Duchy of Lithuania by signing the Union of Lublin. This union formed the Polish–Lithuanian Commonwealth, one of the largest (about 1 million km2) and most populous countries of 16th and 17th centuryEurope, with a uniquely liberal political system which adopted Europe's first written national constitution, the Constitution of 3 May 1791.
More than a century after the Partitions of Poland at the end of the 18th century, Poland regained its independence in 1918 with the Treaty of Versailles. In September 1939, WorldWar II started with the invasion of Poland by Germany, followed by the Soviet Union invading Poland in accordance with the Molotov–Ribbentrop Pact.