Oh guys why you get me staaarted ( Bulgarian Here) Will try the short version. I have also posted in the forum before might try and find it. Anyway.
Slavs migrate to the Balkans couple of centuries before the Bulghars reach the Denube Delta. They have a war with the Bysantines win and have an alliance with the local Slavic tribes what forms the state a.k.a 1st Bulgarian Empire.
There are several debetas about this period. One how much the Bulghars actually were. It ranges between very few compared to the slavs to almost a half of the population. It is believed Bulghars were enough to have a serious military power but also the minority compared to the slavs.
Based on the archeology in the region of the first capital Pliska in that period around half of the graves found bare Bulghar traditions and another half Slav customs. It is likely the Bulghar population was mostly concentrated in that region while the expanse was in regions mostly populated with slavs.
Whatever the ratio between Slavs and Bulghars was in 681 with the expance of the Empire more and more Slavs were joining in the mix. By the 9th century in the Empire there is vast majority of Slavs than Bulghars, Romans and even good number of Avars who became subjects after the fall of the Avar Khaganate. You can say the Bulghars were dominant among the ruling elite and khans are ruling the state until that point while the vast majority of the population were Slavs.
What happens in the 9th and early 10th century is the formation of the Bulgarians as a common group of people. Very important in this process is the official Christianisation. By that time there were some christians in the empire but the pagan traditions were strong among both Slavs and Bulghars. In 866 Boris I adopts Christianity and bans all pagan beliefs. Later he retires and his son Vladimir leads a revold against Christianity. Boris I would return blind his own son, put him in a dungeon and massacre huge number of his son`s supporters (Bulghar noble families). Than put on the throne another of his sons Simeon (The Great).
Another important step is the formation of the medieval Bulgarian script (cyrillic) which is slavic based on local slavic dialects. By the 10th century there are no more Bulghars and Slavs there are Bulgarians. They are christians and have slavic culture. The vast majority of them are with slavic DNA anyway.
I list some fact you may interprete as you wish.
- Bulghars are indeed supposed to be of turkic origin. Not all historians agree but its the dominant hypothesis.
- They always were the minority of the population in medieval Bulgaria while they were the majority of the ruling class.
- By the 10th century based on common religion and written language the Bulgarian people is formed and it has slavic culture.
- As a matter of fact there were 4 states in the Middle ages called Bulgaria. Ăld Great Bulgaria (Bulghars), Volga Bulgaria (Bulghras), First Bulgarian Empire (Bulgarians), Second Bulgaria Empire( Bulgarians). The terms Bulghars and Bulgarians are modern and they only serve the purpose to differenciate between: the turkic, pagan, seminomadic Bulghars from the slavic (castles, Krepost , monastery building, christian) Bulgarians.
