Human activity in the lands of modern Bulgaria can be traced back to the Paleolithic. The earliest examples of symbolic behaviour in humans were unearthed in Kozarnika cave in 2004. These consist of animal bones incised with man-made markings 1.4 million years ago. Organised prehistoric societies in Bulgarian lands include the Neolithic Hamangia culture, Vinča culture and the eneolithic Varna culture (fifth millennium BC). The latter is credited with inventing gold working and exploitation. Some of these first gold smelters produced the coins, weapons and jewellery of the Varna Necropolis treasure, the oldest in the world with an approximate age of over 6,000 years. This site also offers insights for understanding the social hierarchy of the earliest European societies.
One of the three primary ancestral groups of modern Bulgarians were the Thracians, who populated various tribes until king Teres united most of them in the Odrysian kingdom around 500 BC. They were eventually subjugated by Alexander the Great and later by the Roman Empire in 46 AD. After the division of the Roman Empire in 5th century the area fell under Byzantine control. By this time, Christianity had already spread in the area. A small Gothic community in Nicopolis ad Istrum produced the first Germanic language book in the 4th century, the Wulfila Bible. The first Christian monastery in Europe was established around the same time by Saint Athanasius in central Bulgaria. From the 6th century the easternmost South Slavs gradually settled in the region, assimilating the Hellenised or Romanised Thracians.
In the 7th century, Bulgar tribes (likely of central Asian Turkic origin), migrated to the lower courses of the rivers Danube, Dniester and Dniepr under the leadership of Asparukh. After 670 he moved into the Balkan Peninsula with a horde of 50,000 Bulgars across the Danube and in 680 severed Scythia Minor from the Byzantine Empire. A peace treaty with Byzantium in 681 and the establishment of a permanent capital at Pliska south of the Danube marked the beginning of the First Bulgarian Empire. The Bulgars gradually mixed up with the local population, adopting a common language on the basis of Slavonic.
Succeeding khans strengthened the Bulgarian state throughout the 8th and 9th centuries — Tervel established Bulgaria as a major military power by defeating a 26,000-strong Arab army during the Second Arab Siege of Constantinople. Krum doubled the country's territory, killed Byzantine emperor Nicephorus I in the Battle of Pliska, and introduced the first written code of law. In 864 Boris I abolished paganism in favour of Eastern Orthodox Christianity. Simeon the Great's 34-year rule began in 893 and saw the largest territorial expansion of Bulgaria, along with a golden age of Bulgarian culture.
Wars with Croatians, Magyars, Pechenegs and Serbs and the spread of the Bogomil heresy weakened Bulgaria after Simeon's death. Two consecutive Rus' and Byzantine invasions resulted in the seizure of the capital Preslav by the Byzantine army in 971. Under Samuil, Bulgaria somewhat recovered from these attacks and managed to conquer Serbia and Albania, but this rise ended when Byzantine emperor Basil II defeated the Bulgarian army at Klyuch in 1014. Samuil died shortly after the battle, and by 1018 the Byzantines had ended the First Bulgarian Empire.
After his conquest of Bulgaria, Basil II prevented revolts and discontent by retaining the rule of the local nobility and recognising the autocephaly of the Archbishopric of Ohrid. After his death Byzantine domestic policies changed and a series of unsuccessful rebellions broke out, the largest being led by Peter Delyan. In 1185 Asen dynasty nobles Ivan Asen I and Peter IV organised a major uprising which resulted in the re-establishment of the Bulgarian state. Ivan Asen and Peter laid the foundations of the Second Bulgarian Empire with Tarnovo as a capital.
Kaloyan, the third of the Asen monarchs, extended his dominion to Belgrade and Ohrid. He acknowledged the spiritual supremacy of the Pope and received a royal crown from a papal legate. The empire reached its zenith under Ivan Asen II (1218–1241), when commerce and culture flourished. The strong economic and religious influence of Tarnovo made it a "Third Rome", unlike the already declining Constantinople.
The country's military and economic might declined after the Asen dynasty ended in 1257, facing internal conflicts, constant Byzantine and Hungarian attacks and Mongol domination. By the end of the 14th century, factional divisions between the feudal landlords and the spread of Bogomilism had caused the Second Bulgarian Empire to split into three tsardoms—Vidin, Tarnovo and Karvuna—and several semi-independent principalities that fought each other, along with Byzantines, Hungarians, Serbs, Venetians and Genoese. By the late 14th century the Ottoman Turks had started their conquest of Bulgaria and had taken most towns and fortresses south of the Balkan mountains.
Tarnovo was captured by the Ottomans after a three-month siege in 1393. After the Battle of Nicopolis in 1396 brought about the fall of the Vidin Tsardom, the Ottomans conquered all Bulgarian lands south of the Danube. The nobility was eliminated and the peasantry was enserfed to Ottoman masters,[ with much of the educated clergy fleeing to other countries. Under the Ottoman system, Christians were considered an inferior class of people. Thus, Bulgarians, like other Christians, were subjected to heavy taxes and a small portion of the Bulgarian populace experienced partial or complete Islamisation, and their culture was suppressed. Ottoman authorities established the Rum Millet, a religious administrative community which governed all Orthodox Christians regardless of their ethnicity. Most of the local population gradually lost its distinct national consciousness, identifying as Christians. However, the clergy remaining in some isolated monasteries kept it alive, and that helped it to survive as in some rural, remote areas, as well as in the militant Catholic community in the northwestern part of the country.
Several Bulgarian revolts erupted throughout the nearly five centuries of Ottoman rule, most notably the Habsburg-backed Tarnovo uprisings in 1598 and in 1686, the Chiprovtsi Uprising in 1688 and Karposh's Rebellion in 1689. In the 18th century, the Enlightenment in Western Europe provided influence for the initiation of a movement known as the National awakening of Bulgaria. It restored national consciousness and became a key factor in the liberation struggle, resulting in the 1876 April Uprising. Up to 30,000 Bulgarians were killed as Ottoman authorities put down the rebellion. The massacres prompted the Great Powers to take action. They convened the Constantinople Conference in 1876, but their decisions were rejected by the Ottomans. This allowed the Russian Empire to seek a solution by force without risking military confrontation with other Great Powers, as had happened in the Crimean War. In 1877 Russia declared war on the Ottoman empire and defeated its forces with the help of Bulgarian volunteers.
The Treaty of San Stefano was signed on 3 March 1878 by Russia and the Ottoman Empire, and included a provision to set up an autonomous Bulgarian principality roughly on the territories of the Second Bulgarian Empire. It never went into effect, as the Great Powers immediately rejected the treaty out of fear that such a large country in the Balkans might threaten their interests. It was superseded by the subsequent Treaty of Berlin, signed on 13 July, provided for a much smaller state comprising Moesia and the region of Sofia, leaving large populations of Bulgarians outside the new country. This played a significant role in forming Bulgaria's militaristic approach to foreign affairs during the first half of the 20th century.
The Bulgarian principality won a war against Serbia and incorporated the semi-autonomous Ottoman territory of Eastern Rumelia in 1885, proclaiming itself an independent state on 5 October 1908. In the years following independence, Bulgaria increasingly militarised and was often referred to as "the Balkan Prussia". Between 1912 and 1918, Bulgaria became involved in three consecutive conflicts—two Balkan Wars and World War I. After a disastrous defeat in the Second Balkan War, Bulgaria again found itself fighting on the losing side as a result of its alliance with the Central Powers in World War I. Despite fielding more than a quarter of its population in a 1,200,000-strong army and achieving several decisive victories at Doiran and Dobrich, the country capitulated in 1918. The war resulted in significant territorial losses, and a total of 87,500 soldiers killed. More than 253,000 refugees emigrated to Bulgaria from 1912-1929 due to the effects of these wars, placing additional strain on the already ruined national economy.
The political unrest resulting from these losses led to the establishment of a royal authoritarian dictatorship by tsar Boris III (1918–1943). Bulgaria entered World War II in 1941 as a member of the Axis but declined to participate in Operation Barbarossa and saved its Jewish population from deportation to concentration camps. The sudden death of Boris III in the summer of 1943 pushed the country into political turmoil as the war turned against Germany and the Communist guerrilla movement gained momentum. The government of Bogdan Filov subsequently failed to achieve peace with the Allies. Bulgaria did not comply with Soviet demands to expel German forces from its territory, resulting in a declaration of war and an invasion by the USSR in September 1944. The Communist-dominated Fatherland Front took power, ended participation in the Axis and joined the Allied side until the war ended.
The left-wing uprising of 9 September 1944 led to the abolition of monarchic rule, but it was not until 1946 that a single-party people's republic was established. It became a part of the Soviet sphere of influence under the leadership of Georgi Dimitrov (1946–1949), who laid the foundations for a rapidly industrialising stalinist state. By the mid-1950s standards of living rose significantly, while political repressions were lessened. By the 1980s both national and per capita GDP quadrupled, but the economy remained prone to debt spikes, the most severe taking place in 1960, 1977 and 1980. The Soviet-style planned economy saw some market-oriented policies emerging on an experimental level under Todor Zhivkov (1954–1989). His daughter Lyudmila bolstered national pride by promoting Bulgarian heritage, culture and arts worldwide. In an attempt to erase the identity of the ethnic Turk minority, an assimilation campaign was launched in 1984. This resulted in the emigration of some 300,000 of them to Turkey.
Under the influence of the collapsing Eastern Bloc, on 10 November 1989 the Communist Party gave up its political monopoly, Zhivkov resigned, and Bulgaria embarked on a transition to a parliamentary democracy. The first free elections in June 1990 were won by the Bulgarian Socialist Party (BSP, the freshly renamed Communist Party). A new constitution that provided for a relatively weak elected President and for a Prime Minister accountable to the legislature was adopted in July 1991. The new system initially failed to improve living standards or create economic growth—the average quality of life and economic performance remained lower than under Communism well into the early 2000s. A 1997 reform package restored economic growth, but living standards continued to suffer. After 2001 economic, political and geopolitical conditions improved greatly, and Bulgaria achieved high Human Development status. It became a member of NATO in 2004 and of the European Union in 2007.