What was common in the history of formation and the beginning of the existence of the Slavic states?

What they had in common was the existence of paganism, that is, certain religious beliefs, the existence of a state structure, common traditions, a close language, and so on. One of the first Slavic states was the Bulgarian kingdom. It arose back in 681. At that time, it was a fairly strong state formation. True, over time, Byzantium was able to conquer Bulgaria and annex her lands. The most powerful was the state of Kievan Rus, which arose in 862.