The Principality of Bulgaria was a vassal state under the suzerainty of the Ottoman Empire. It was established by the Treaty of Berlin in 1878.

Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. Located west of the Black Sea and south of the Danube river, Bulgaria is bordered by Greece and Turkey to the south, Serbia and North Macedonia to the west, and Romania to the north. It covers a territory of 110,994 square kilometres (42,855 sq mi) and is the 16th largest country in Europe. Sofia is the nation's capital and largest city; other major cities include Burgas, Plovdiv, and Varna.