Bulgaria (-/ ( listen); Bulgarian: България, tr. Bǎlgariya), officially the Republic of Bulgaria (Bulgarian: Република България, tr. Republika Bǎlgariya, IPA: [rɛˈpublikɐ bɐɫˈɡarijɐ]), is a country in southeastern Europe. It is bordered by Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, and the Black Sea to the east. The capital and largest city is Sofia; other major cities are Plovdiv, Varna and Burgas. With a territory of 110,994 square kilometres (42,855 sq mi), Bulgaria is Europe's 16th-largest country.
In the Neolithic period, organized prehistoric cultures appeared in the lands that would one day become Bulgaria. In Antiquity (6th–3rd century BC), the region became a battleground for Thracians, Persians, Celts and Macedonian Greeks until it was conquered by the Roman Empire in 45 AD. The Eastern Roman, or Byzantine, Empire lost some of these territories to an invading Bulgar horde in the late 7th century. The Bulgars then founded the first unified Bulgarian state in 681 AD which dominated most of the Balkans and functioned as a cultural hub for Slavs during the Middle Ages. The First Bulgarian Empire lasted until the early 11th century, when Byzantine emperor Basil II conquered and dismantled it. A successful Bulgarian revolt in 1185 established a Second Bulgarian Empire which reached its apex under Ivan Asen II (1218–1241). After numerous exhausting wars and feudal strife, the Second Bulgarian Empire disintegrated in 1396 and its territories fell under Ottoman rule for nearly five centuries. The Russo-Turkish War of 1877–78 resulted in the formation of the current Third Bulgarian State. Many ethnic Bulgarian populations were left outside its borders, which led to several conflicts with its neighbours and an alliance with Germany in both world wars. In 1946 Bulgaria became a one-party socialist state and part of the Soviet-led Eastern Bloc. The ruling Communist Party gave up its monopoly on power after the Revolutions of 1989 and allowed multi-party elections. Bulgaria then transitioned into a democracy and a market-based economy.
Since the adoption of a democratic constitution in 1991, Bulgaria has functioned as a unitary parliamentary republic with a high degree of political, administrative, and economic centralisation. Most commercial and administrative activities are concentrated in its capital and largest city of Sofia. The predominantly urbanized population of seven million people mainly inhabits the primary cities of the 28 provinces. Bulgaria's market economy is part of the European Single Market and is largely based on services, agriculture, and a sizeable industrial sector focused on mining and machine building.
Bulgaria is a member of the European Union, NATO, and the Council of Europe; it is a founding state of the Organization for Security and Co-operation in Europe (OSCE) and has taken a seat at the UN Security Council three times. It is also notable for its biodiversity, its achievements in sports and science, particularly space exploration, and its historical influence on Slavic cultures through its Medieval literary schools and the Cyrillic script. However, it continues to struggle with crippling corruption and severe demographic decline.
The name Bulgaria is derived from the Bulgars, a tribe of Turkic origin that established the country. Their name is not completely understood and difficult to trace back earlier than the 4th century AD, but it is possibly derived from the Proto-Turkic word bulģha ("to mix", "shake", "stir") and its derivative bulgak ("revolt", "disorder"). The meaning may be further extended to "rebel", "to incite", or "to produce a state of disorder", i.e. the "disturbers". "To mix" or "of mixed stock" is a disputed interpretation of the word referring to the supposed mixing of the Oghurs and the Huns that initiated the Bulgars' ethnogenesis. Such mixing, however, may have occurred earlier. Scholar Sanping Chen has noted analogous groups in Inner Asia, with phonologically similar names, who were frequently described in similar terms: during the 4th century, the Buluoji, a component of the "Five Barbarian" groups in Ancient China, were portrayed as both a "mixed race" and "troublemakers". Alternate etymologies include derivation from a compound of Proto-Turkic bel ("five") and gur ("arrow" in the sense of "tribe"), a proposed division within the Utigurs or Onogurs ("ten tribes").