Lithuania is a country in Europe's Baltic region, officially known as the Republic of Lithuania. It is one of the Baltic states, located on the Baltic Sea's eastern coast, southeast of Sweden and east of Denmark, with Latvia to the north, Belarus to the east and south, Poland to the south, and Russia's Kaliningrad Oblast to the southwest. Lithuania has a population of 2.7 million people and a land area of 65,300 km2. Vilnius is the country's capital and largest city; Kaunas and Klaipda are also important cities. Lithuanians are part of the Balt ethnolinguistic community and speak Lithuanian, which is one of only two living Baltic languages. Various Baltic tribes populated the southeastern coasts of the Baltic Sea for centuries. Mindaugas unified the Lithuanian lands in the 1230s, and the Kingdom of Lithuania was founded on July 6, 1253. The Grand Duchy of Lithuania was the largest nation in Europe in the 14th century, encompassing modern-day Lithuania, Belarus, Ukraine, and parts of Poland and Russia. With the Lublin Union of 1569, Lithuania and Poland created the Polish–Lithuanian Commonwealth, a mutual two-state personal union. The Commonwealth lasted more than two centuries, until it was dissolved by neighboring countries in 1772–1795, with the Russian Empire annexing the majority of Lithuania's land. On February 16, 1918, as World War I drew to a close, Lithuania's Act of Independence was signed, establishing the modern Republic of Lithuania. Lithuania was invaded twice during WWII, first by the Soviet Union and then by Nazi Germany. The Soviet Union reoccupied Lithuania as World War II drew to a close and the Germans withdrew. Lithuania became the first Baltic state to declare independence on March 11, 1990, a year before the official breakup of the Soviet Union, under the name of the State of Lithuania. Lithuania is a developing nation with a high-income advanced economy, ranking very high in the Human Development Index. In terms of civil rights, press freedom, and internet freedom, it scores well. However, since the 1990s, Lithuania has seen a steady population decline, with social problems such as income inequality and a high suicide rate persisting. Lithuania is a member of the European Union, the Council of Europe, the eurozone, the Nordic Investment Bank, the Schengen Agreement, NATO, and the Organization for Economic Cooperation and Development. It is a member of the Nordic-Baltic Eight format of regional cooperation.