Bulgaria shares borders with Serbia, Macedonia, Romania, Greece, and Turkey. Two mountain ranges and two great valleys mark the topography of Bulgaria, a country the size of Tennessee and situated on the Black Sea. The Danube is the principal river that runs through the border between Romania and Bulgaria.

Ancient Thrace and Moesia, which modern Bulgaria occupies, were settled (6th cent. A.D.) by Slavic tribes. In 679–80, Bulgar tribes from the banks of the Volga crossed the Danube, subjugated the Slavs, and settled permanently in the territory of Bulgaria. The language and culture remained Slavic, and by the 9th century the Bulgars had fully merged with the Slavs. Although the country bears the name of the Bulgars, the Bulgar language and culture died out, replaced by a Slavic language, writing, and religion. In 865, Boris I adopted Orthodox Christianity, and in 870 Constantinople recognized the independence of the Bulgarian church. Bulgaria received Byzantine culture through the Slavic literary language developed by St. Cyril and St. Methodius in Moravia and brought to the Balkans by their disciples.

The first Bulgarian empire reached its height under Simeon I (893–927), who took the title of czar. In 1396 they were invaded by the Ottoman Empire, which made Bulgaria a Turkish province until 1878. Ottoman rule was harsh and inescapable, given Bulgaria's proximity to its oppressor. In 1878, Russia forced Turkey to give Bulgaria its independence after the Russo-Turkish War (1877–1878). A Soviet-style People's Republic was established in 1947 and Bulgaria acquired the reputation of being the most slavishly loyal to Moscow of all the East European Communist countries.

In Oct. 1991, the Union of Democratic Forces won, forming Bulgaria's first non-Communist government since 1946. Power shifted back and forth between the pro-Western Union of Democratic Forces (UDF) and the BSP during the 1990s. In July 2001, the former king of Bulgaria; Simeon Saxe-Coburg-Gotha (Simeon II), became the new prime minister. He had been dethroned 55 years earlier (at age nine) during the Communist takeover of the country. Bulgaria became a member of NATO in 2004. In 2005, the EU approved Bulgaria's membership for 2007.