Poland, officially the Republic of Poland, is a country located in Central Europe, between Germany to the west, the Czech Republic and Slovakia to the south, Ukraine and Belarus to the east, and the Baltic Sea, Lithuania, and Russia to the north. Poland shares a maritime border with Denmark in the Baltic Sea. Poland has been a member state of the European Union since May 1, 2004.
The Polish state was formed over 1,000 years ago under the Piast dynasty, and reached its golden age near the end of the 16th century under the Jagiellonian dynasty, when Poland was one of the largest, wealthiest, and most powerful countries in Europe. In 1791 the Sejm of the Polish-Lithuanian Commonwealth adopted the Constitution of May 3, Europe's first modern codified constitution, and the second in the world after the Constitution of the United States. Soon afterwards, the country ceased to exist after being partitioned by its neighbours Russia, Austria, and Prussia. It regained independence in 1918 in the aftermath of the First World War as the Second Polish Republic. Following the Second World War it became a communist satellite state of the Soviet Union known as the People's Republic of Poland. In 1989 the first partially-free elections in Poland's post-World War II history concluded the Solidarity movement's struggle for freedom and resulted in the defeat of Poland's communist rulers. The current Third Polish Republic was established, followed a few years later by the drafting of a new constitution in 1997. In 1999 Poland acceded to NATO, and in 2004 it joined the European Union.