Poland, officially the Republic of Poland is a country in Central Europe. Poland is bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north. The total area of Poland is 312,679 km² (120,728 sq mi), making it the 69th largest country in the world and 9th in Europe. Poland has a population of over 38.5 million people, which makes it the 33rd most populous country in the world. The establishment of a Polish state is often identified with the adoption of Christianity by its ruler Mieszko I in 966, when the state covered territory similar to that of present-day Poland. Poland became a kingdom in 1025, and in 1569 it cemented a long association with the Grand Duchy of Lithuania by uniting to form the Polish-Lithuanian Commonwealth.