Claim: Poland is ranked on the Human Development Index.

Poland -LRB- Polska -LSB- ˈpɔlska -RSB- -RRB- , officially the Republic of Poland -LRB- -LSB- Rzeczpospolita Polska , links = no -RSB- , -RRB- , is a parliamentary republic in Central Europe . Poland is a unitary state divided into 16 administrative subdivisions , covering an area of 312679 km2 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 cities include Kraków , 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 declared Europe 's first constitution .   Following 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 , World War II started with the invasion of Poland by Nazi Germany , followed by the Soviet Union invading Poland in accordance with the Molotov -- Ribbentrop Pact . More than six million of Poland 's citizens died in the war . After World War II , the Polish People 's Republic was established as a satellite state under Soviet influence . In the aftermath of the Revolutions of 1989 , most notably through the emergence of the Solidarity movement , Poland established itself as a democratic republic .   Poland is the eighth largest and one of the most dynamic economies in the European Union , simultaneously achieving a `` very high '' ranking on the Human Development Index . Additionally , the Polish Stock Exchange in Warsaw is the largest and most important in Central and Eastern Europe . Poland is a developed and democratic country , with a high-income economy , and a very high standard of living . It also ranks very highly in education , safety and economic freedom . According to the World Bank , Poland has one of the best educational systems in Europe , placing it among the most educated nations . The country provides free university education , state-funded social security and a universal health care system for all citizens . Situated between Eastern and Western European cultures and coined by a changing history , Poland developed a rich cultural heritage , including numerous historical monuments and 14 UNESCO World Heritage Sites . It is visited by approximately 16 million tourists every year -LRB- 2014 -RRB- , making it the 16th most visited country in the world . Poland is a member state of the European Union , the Schengen Area , the United Nations , NATO and the OECD .