Poland officially the Republic of Poland is a country in East-Central Europe, bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus to the east; and the Baltic Sea and Kaliningrad Oblast (a Russian exclave) and Lithuania to the north. The total area of Poland is 312,679 square kilometres (120,726 sq mi), making it the 69th largest country in the world and the 9th largest in Europe. With a population of over 38.5 million people, Poland is the 34th most populous country in the world, the sixth most populous member of the European Union, and the most populous post-communist member of the European Union. Poland is a unitary state divided into 16 administrative subdivisions.
Many historians trace the establishment of a Polish state to 966, when Mieszko I, ruler of a territory roughly coextensive with that of present-day Poland, converted to Christianity. The Kingdom of Poland was founded in 1025, and in 1569 it cemented a longstanding political association with the Grand Duchy of Lithuania by signing the Union of Lublin, forming the Polish–Lithuanian Commonwealth. The Commonwealth gradually ceased to exist in the years 1772-1795, when the Polish territory was partitioned among Germany, the Russian Empire, and Austria. Poland regained its independence (as the Second Polish Republic) at the end of World War I, in 1918.
Two decades later, in September 1939, World War II started with the invasions of Poland by Nazi Germany and the Soviet Union (as part of the Molotov–Ribbentrop Pact). More than six million Polish citizens died in the war. In 1944, the Polish People's Republic was proclaimed and after a brief period of conflict, falsified referendum and elections Poland became a satellite state of the Soviet Union in 1947, and was accordingly renamed the People's Republic of Poland in 1952. During the Revolutions of 1989, Poland's communist government was overthrown and Poland adopted a new constitution establishing itself as a democracy and renaming itself the "Third Polish Republic".
Despite the vast destruction the country experienced during World War II, Poland managed to preserve much of its cultural wealth. There are 14 heritage sites inscribed on the UNESCO World Heritage list in Poland and 54 Historical Monuments. Since the end of the communist period, Poland has achieved a "very high" ranking in terms of human development.