Bulgaria, is a country located 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. With a territory of 110,994 square kilometres (42,855 sq mi), Bulgaria is Europe's 14th-largest country.
Prehistoric cultures began developing on Bulgarian lands during the Neolithic period. Its ancient history saw the presence of the Thracians, and later the Greeks and Romans. The emergence of a unified Bulgarian state dates back to the establishment of the First Bulgarian Empire in 681 AD, which dominated most of the Balkans and functioned as a cultural hub for Slavic peoples during the Middle Ages. With the downfall of the Second Bulgarian Empire in 1396, its territories came under Ottoman rule for nearly five centuries. The Russo-Turkish War of 1877–1878 created the Third Bulgarian State. The following years saw several conflicts with its neighbours, which prompted Bulgaria to align with Germany in both World Wars. In 1946 it became a Socialist state with a single-party system. In 1989 the Communist Party allowed multi-party elections, following which Bulgaria transitioned to democracy and a market-based economy.
The population of 7.36 million people is predominantly urban and mainly concentrated in the administrative centres of its 28 provinces. Most commercial and cultural activities are concentrated in the capital Sofia. The strongest sectors of the economy are heavy industry, power engineering, and agriculture, all relying on local natural resources.
The current political structure dates to the adoption of a democratic constitution in 1991. Bulgaria is a unitary parliamentary republic with a high degree of political, administrative, and economic centralisation. It is a member of the European Union, NATO, and the Council of Europe; 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.
One of the three primary ancestral groups of modern Bulgarians were the Thracians, who populated various tribes until king Teres united most of them in the Odrysian kingdom around 500 BC. They were eventually subjugated by Alexander the Great and later by the Roman Empire in 46 AD. After the division of the Roman Empire in 5th century the area fell under Byzantine control. By this time, Christianity had already spread in the area. A small Gothic community in Nicopolis ad Istrum produced the first Germanic language book in the 4th century, the Wulfila Bible. The first Christian monastery in Europe was established around the same time by Saint Athanasius in central Bulgaria. From the 6th century the easternmost South Slavs gradually settled in the region, assimilating the Hellenised or Romanised Thracians.