By the 4th century the major city of Serdica had predominantly Thracian populace based on epigraphic evidence, which shows prevailing Latino-Thracian given names, but thereafter the names were completely replaced by Christian ones.The Early Slavs emerged from their original homeland in the early 6th century, and spread to most of the eastern Central Europe, Eastern Europe and the Balkans, thus forming three main branches: the West Slavs in eastern Central Europe, the East Slavs in Eastern Europe, and the South Slavs in Southeastern Europe (Balkans).Orthodox Christians were included in a specific ethno-religious community called Rum Millet.To the common people, belonging to this Orthodox commonwealth became more important than their ethnic origins.The rise of nationalism under the Ottoman Empire led to a struggle for cultural and religious autonomy of the Bulgarian people.The Bulgarians wanted to have their own schools and liturgy in Bulgarian, and they needed an independent ecclesiastical organisation.The Bulgars are first mentioned in the 4th century in the vicinity of the North Caucasian steppe.
A symbiosis was carried out between the numerically weak Bulgars and the numerous Slavic tribes in that broad area from the Danube to the north, to the Aegean Sea to the south, and from the Adriatic Sea to the west, to the Black Sea to the east, who accepted the common ethnonym "Bulgarians".
The Thracian language has been described as a southern Baltic language.
According to archeological evidence from the late periods of Roman rule, the Romans did not decrease the number of Thracians significantly in major cities.
Some Bulgarians supported the Russian Army when they crossed the Danube in the middle of the 18th century.
Russia worked to convince them to settle in areas recently conquered by it, especially in Bessarabia.