Bulgaria 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. With a territory of 110，994 square kilometers and a population of 7 million in 2019， Bulgaria is Europe's 16th-largest country. Organized prehistoric cultures began developing on current Bulgarian lands during the Neolithic period. Its ancient history saw the presence of the Thracians， Greeks and Romans. The emergence of a unified Bulgarian state dates back to the establishment of the First Bulgarian Empire in 681， which dominated most of the Balkans and functioned as a cultural hub for Slavs 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 led to the formation of the Third Bulgarian State. The following years saw several conflicts with its neighbors， which prompted Bulgaria to align with Germany in both world wars. It now is a member of the European Union， NATO and the Council of Europe; a founding state of the Organization for Security and Cooperation in Europe （OSCE）; and has taken a seat at the UN Security Council three times. Bulgaria and China are traditional friendly countries. There is profound friendship with solid social basis between the two countries and peoples. Bulgaria has actively participated in China's Belt and Road Initiative.