In 680 Bulgar tribes, under the leadership of Asparukh moved south across the Danube and settled in the area between the lower Danube and the Balkans. A peace treaty with Byzantium in 681 marked the beginning of the first Bulgarian Empire. The Bulgars gradually mixed up with the local population, adopting a common Slavic-based language. Future rulers strengthened the Bulgarian state throughout the 8th and 9th centuries. Krum doubled the country's territory, killed Byzantine emperor Nicephorus I in the Battle of Pliska, and introduced the first written Bulgar code of law. Under Boris I, Bulgarian paganism was abolished in favor of Eastern Orthodoxy. This conversion was recognized by the Byzantine church and the adoption of the Cyrillic alphabet, which strengthened authority and helped unify the Slavs and Bulgars. A subsequent cultural golden age began during the 34-year rule of Simeon the Great, who also achieved the largest territorial expansion of the state. Consecutive Rus' and Byzantine invasions resulted in the seizure of the capital Preslav by the Byzantine army in 971. Bulgaria briefly recovered from these attacks, but by 1018 the Byzantines conquered the first Bulgarian Empire. After his conquest of Bulgaria, Basil II prevented revolts and discontent by retaining the rule of the local nobility and by relieving the newly conquered lands of the obligation to pay taxes in gold, allowing them to be paid in kind instead. 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. Under the Second Bulgarian Empire, Bulgaria hit its zenith and a cultural golden age occurred; Tarnovo became known as the "Third Rome" under this imperial rule. However, by the end of the 14th century and invasions from surrounding empires, the Second Bulgarian Empire split into three tsardoms which were later conquered by the Ottoman Empire.
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 Bulgarian nobility was eliminated and the peasantry was enserfed to Ottoman mastered. Much of the educated Bulgarian clergy fled to other nations. 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, with the help of cultural suppression. However, the clergy remaining in some isolated monasteries helped Catholicism survive in some rural areas of Bulgaria. Several Bulgarian revolts erupted throughout the nearly five centuries of Ottoman rule, although the Bulgarians were never able to obtain sovereignty. The Enlightenment created a movement known as the National awakening of Bulgaria, which restored national consciousness and became a key factor in liberating Bulgaria, resulting in the 1876 April Uprising. In 1877, Russia declared war on the Ottoman Empire with help from various South Slavic volunteers, including Bulgarians.
Bulgaria never received true independence from the Ottomans after this war, however the new Bulgarian principality won a war against Serbia and incorporated the semi-autonomous Ottoman territory of Eastern Rumelia in 1885, proclaiming itself the independent Tsardom of Bulgaria on 5 October 1908. In the years following independence, Bulgaria increasingly militarized. Bulgaria fought in both the Balkan Wars and the World War; Bulgaria lost the latter two. The political unrest resulting from these losses led to the establishment of a royal authoritarian dictatorship by tsar Boris III. A left-wing uprising in 1944 forced Boris to abdicate, creating a constitutional monarchy in Bulgaria. Today, Bulgaria is a democratic state with a stable economy.