Bulgaria is a republic in Southeastern Europe, bordered by five other countries; Romania to the north (mostly along the Danube), Serbia and the Republic of Macedonia to the west, and Greece and Turkey to the south. It is bordered by the Black Sea to the east.
Bulgaria has been the center of two medieval empires (AD 632-1018 and 1185 to 1396), as well as the subject of foreign empires (Byzantine Empire, 1018-1185; Ottoman Empire, 1396-1877). The Third Bulgarian state was established in 1877 as an autonomous principality within the Ottoman Empire, until full independence was established in 1908 as a constitutional monarchy. However, many Bulgarians still resided outside of the borders of Bulgaria proper. This state of affairs, combined with various claims of other countries in the region, led to the two Balkan Wars of 1912 and 1913. While Bulgaria was on the winning side of the first war, it was defeated during the second, and still was not quite unified.
Bulgaria joined World War I on the side of the Central Powers in an effort to bring a final unity, but was defeated. In an effort to finally unify, Bulgaria sided with the Axis during World War II. As the SovietRed Army bore down throughout 1943 and 1944, Bulgaria withdrew from the war, and attempted to declare war on Germany. This was too little too late; the Soviets entered, and immediately began laying the foundation for a communist state. In 1946, rigged elections lead to the creation of the People's Republic of Bulgaria. One-party rule ended in 1990 after the Bulgarian Communist Party moved to the center-left and allowed free and open elections, bringing the People's Republic to an end.
Bulgaria has remained a stable unitary parliamentary republic since 1991. It is a member of NATO and the European Union.
The Eastern Roman Empire, whose eastern border with the Persian Empire had remained more or less stable for over a thousand years and which faced no major threats from this direction, was able to hold on to the full territory up to the Danube River which it had inherited from the original Western Roman Empire. In the 13th century, Byzantine soldier and spy Basil Argyros recalled the Bulgars as a past invading nomadic people who in their time posed a significant threat to the Empire, but which were eventually overcome and left no permanent trace of their invasion.
The People's Republic of Bulgaria followed the Soviet Union into World War III, and then followed many Soviet satellites into rebellion against Communist rule. In August, 1952, Soviet naval infantry successfully invaded Bulgaria via the Black Sea as part of an operation to bring Bulgaria to heel.
The Bulgar Khan Telerikh came to the conclusion that he could not go on practicing the religion of his ancestors, and had to accept one of the two competing monotheistic religions, thus gaining its adherants' alliance against the other one. Accordingly, he invited Muslim and Christian emissaries to present their religious doctrines to himself and his courtiers.
However, while listening patiently and at length to both delegations, the Khan's ultimate decision to convert to Islam was in essence derived less from theological considerations and more from geo-political ones; Islam was the stronger and more powerful political and military force. Bulgaria was the first country which converted to Islam by the voluntary decision of its ruler rather than through conquest by Islamic armies.
The conversion of Bulgaria stood for the proposition that henceforth, Islam would grow and Christianity would shrink. The dismayed Christian missionaries at Telerikh's court realized as much at the moment itself.
During the Second Great War, the early Entente victories saw Bulgaria waver in its allegiance to the Central Powers, though the presence of Germany's ally, the Ottoman Empire on its southern border persuaded the Bulgarians to remain associated with Germany.