Bulgaria or the Republic of Bulgaria ( Bulgarian : Република България ) is a southeastern European country bordering the Black Sea on its western side. It is bordered by Romania to the north , Turkey and Greece to the south, and the Republic of Serbia and the Republic of Macedonia to the west. With an area of 110,994 square kilometers (42,855sq mi), Bulgaria is the 16th largest country in Europe.
Prehistoric cultures began settlement in the territory of Bulgaria during the Neolithic period. Its ancient history saw the Thracians and later Greece and the Roman Empire . The emergence of a unified Bulgarian state dates back to the founding of the first Bulgarian Empire in 681, which ruled most of the Balkans and served as a cultural center for the Slavs during the Middle Ages . With the fall of the Second Bulgarian Empire in 1396, its territories came under the control of the Ottoman Empire for nearly centuries.
The Russian-Ottoman War (1853 - 1856) led to the formation of the third Bulgarian state. In subsequent years Bulgaria experienced several conflicts with its neighbors, prompting an alliance with Germany in World Wars I and II . In 1946 Bulgaria became a single partisan socialist state led by the Soviet Union ( Eastern Bloc ).
In December 1989, the ruling Bulgarian Communist Party allowed multi-party elections that led to Bulgaria becoming a democratic state and an economic market center.
It joined the European Union on 1 January 2007 .