Poland, officially the Republic of Poland, is a unitary sovereign state in Central Europe. It is divided into 16 administrative subdivisions, covering an area of 312,679 square kilometres with a mostly temperate climate. With a population of over 38.5 million people, Poland is the sixth most populous member state of the European Union. Poland's capital and largest city is Warsaw. Other major cities include Kraków, Łódź, Wrocław, Poznań, Gdańsk and Szczecin.
The establishment of a Polish state can be traced back 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. This union formed the Polish–Lithuanian Commonwealth, one of the largest and most populous countries of 16th and 17th century Europe, with a uniquely liberal political system which adopted Europe's first written national constitution, the Constitution of 3 May 1791.