Bulgaria (Bulgarian: България, tr. Bŭlgariya, IPA: [bɤ̞ɫˈɡarijɐ]), officially the Republic of Bulgaria (Република България, tr. Republika Bŭlgariya, IPA: [rɛˈpublikɐ bɤ̞ɫˈɡarijɐ]), is a parliamentary republic in Southeast Europe. It borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east. Bulgaria is a very mountainous country due to its location in the Balkan peninsula. With a territory of 92,978 square kilometres, Bulgaria ranks as the 15th-largest country in Europe.
Prehistoric cultures began developing on Bulgarian lands during the Neolithic period. Its ancient history has been marked by the presence of the Thracians, and later by the Greeks and Romans. The emergence of a unified Bulgarian ethnicity and state dates back to the seventh century and the First Bulgarian Empire, which functioned as a cultural hub for Slavic peoples and spread over most of the Balkans during the Middle Ages. With the downfall of the Second Bulgarian Empire in 1396, its territories came under Ottoman rule for nearly five hundred years. The Russo-Turkish War of 1877–1878 resulted in the Third Bulgarian State, recognised in 1908. Shortly afterward, Bulgaria engaged in a series of major conflicts with its neighbours and allied with Germany in both World Wars. In 1946 it became a communist republic and it was a satellite member of the Warsaw Pact until 1989, when the Communist Party allowed multi-party elections. After 1990 Bulgaria transitioned to democracy and introduced free-market capitalism.
The current political structure dates to the adoption of a democratic constitution in 1991. Bulgaria is a member of the European Union, NATO, the Council of Europe, a founding state of the OSCE, and has been a member of the UN Security Council three times. It is a unitary state with a high degree of political, administrative and economic centralisation, and it is considered a free country.
The population of 7.36 million people is predominantly urban and mainly concentrated in the administrative centres of its 28 provinces. With 1.5 million people, the capital Sofia is the largest city and concentrates most commercial and cultural activities. The strongest sectors of the economy are heavy industry, power engineering and agriculture, all relying on local natural resources.
As a historical crossroad for various civilisations, Bulgaria is the home of some of the most ancient cultural artifacts in the world.