What was the difference between the social system of the Slavs and the structure of the Byzantine Empire?

The ancient Slavs chose a leader, while in the Byzantine Empire the emperor appointed his successor and his power was absolute and indisputable. However, over time, among the Slavs, individual people began to advance, who became princes and boyars. The ancient Slavs were personally free, lived in communities or families, the citizens of the empire were considered servants (or even slaves) of the Byzantine emperor. Slaves were not widespread among the ancient Slavs, unlike the Byzantine Empire, where slavery was replaced by a colonial.