Bulgaria the Republic of Bulgaria, is a country in Southeast Europe. It is bordered by Romania to the north and North Macedonia to the west and Turkey to the south, the Black Sea to the east; the capital and largest city is Sofia. With a territory of 110,994 square kilometres, Bulgaria is Europe's 16th-largest country. One of the earliest societies in the lands of modern-day Bulgaria was the Neolithic Karanovo culture, which dates back to 6,500 BC. In the 6th to 3rd century BC the region was a battleground for Thracians, Persians and ancient Macedonians; the Eastern Roman, or Byzantine, Empire lost some of these territories to an invading Bulgar horde in the late 7th century. The Bulgars founded the First Bulgarian Empire in AD 681, which dominated most of the Balkans and influenced Slavic cultures by developing the Cyrillic script; this state 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.
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 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 transitioned into a democracy and a market-based economy. Since adopting a democratic constitution in 1991, the sovereign state has been a unitary parliamentary republic with a high degree of political and economic centralisation; the population of seven million lives in Sofia and the capital cities of the 27 provinces, the country has suffered significant demographic decline since the late 1980s.
Bulgaria is a member of the European Union, NATO, the Council of Europe. Its market economy is part of the European Single Market and relies on services, followed by industry—especially machine building and mining—and agriculture. Widespread corruption is a major socioeconomic issue; the name Bulgaria is derived from a tribe of Turkic origin that founded the country. Their name is not understood and difficult to trace back earlier than the 4th century AD, but it is derived from the Proto-Turkic word bulģha and its derivative bulgak; the meaning may be further extended to "rebel", "incite" or "produce a state of disorder", i.e. the "disturbers". Ethnic groups in Inner Asia with phonologically similar names were 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". Neanderthal remains dating to around 150,000 years ago, or the Middle Paleolithic, are some of the earliest traces of human activity in the lands of modern Bulgaria.
The Karanovo culture arose circa 6,500 BC and was one of several Neolithic societies in the region that thrived on agriculture. The Copper Age Varna culture is credited with inventing gold metallurgy; the associated Varna Necropolis treasure contains the oldest golden jewellery in the world with an approximate age of over 6,000 years. The treasure has been valuable for understanding social hierarchy and stratification in the earliest European societies; the Thracians, one of the three primary ancestral groups of modern Bulgarians, appeared on the Balkan Peninsula some time before the 12th century BC. The Thracians excelled in metallurgy and gave the Greeks the Orphean and Dionysian cults, but remained tribal and stateless; the Persian Achaemenid Empire conquered most of present-day Bulgaria in the 6th century BC and retained control over the region until 479 BC. The invasion became a catalyst for Thracian unity, the bulk of their tribes united under king Teres to form the Odrysian kingdom in the 470s BC.
It was weakened and vassalized by Philip II of Macedon in 341 BC, attacked by Celts in the 3rd century, became a province of the Roman Empire in AD 45. By the end of the 1st century AD, Roman governance was established over the entire Balkan Peninsula and Christianity began spreading in the region around the 4th century; the Gothic Bible—the first Germanic language book—was created by Gothic bishop Ulfilas in what is today northern Bulgaria around 381. The region came under Byzantine control after the fall of Rome in 476; the Byzantines were engaged in prolonged warfare against Persia and could not defend their Balkan territories from barbarian incursions. This enabled the Slavs to enter the Balkan Peninsula as marauders through an area between the Danube River and the Balkan Mountains known as Moesia; the interior of the peninsula became a country of the South Slavs, who lived under a democracy. The Slavs assimilated the Hellenized and Gothicized Thracians in the rural areas. Not l