Estonia is a country in Northern Europe that is officially known as the Republic of Estonia. To the north, the Gulf of Finland separates it from Finland, to the west, the Baltic Sea separates it from Sweden, to the south, Latvia, and to the east, Lake Peipus separates it from Russia. Estonia's jurisdiction consists of the mainland and 2,222 islands off the Baltic Sea's eastern shore, covering a total area of 45,227 km2. It has a humid continental climate. Tallinn, Estonia's capital, and Tartu are the country's two main cities and urban areas. Narva, Pärnu, Kohtla-Järve, and Viljandi are also notable towns. Estonian, the country's official language, is the second most widely spoken Finnic language. Since at least 9,000 BC, the Estonian peninsula has been inhabited. Following the Livonian Crusade in the 13th century, ancient Estonians were some of the last European pagans to convert to Christianity. In the 19th and early 20th centuries, a distinct Estonian national identity began to emerge after centuries of successive rule by Germans, Danes, Swedes, Poles, and Russians. After a brief War of Independence at the end of World War I, Estonians led by General Laidoner had to fight for their newfound freedom, the country was granted independence from Russia in 1920. Estonia, which had been democratic prior to the Great Depression, was ruled by an oppressive regime beginning in 1934, known as the Era of Silence. During World War II, Estonia was repeatedly contested and occupied by Germany and the Soviet Union, eventually being absorbed into the latter as the Estonian SSR. After losing its de facto independence to the Soviet Union, diplomatic representatives and the government-in-exile maintained Estonia's de jure state continuity. After the peaceful Singing Revolution in 1987, the country's de facto independence was restored on August 20, 1991. Estonia is a developing nation with a high-income industrialized economy and a Human Development Index score of 100. The sovereign state is organized into fifteen counties and is a democratic unitary parliamentary republic. It is one of the least populous members of the European Union, the Eurozone, the OECD, the Schengen Area, NATO, and the United Nations Security Council, with a population of 1.3 million.