What are the features of the process of development by the Eastern Slavs of the plains of Eastern Europe?

It is known that in the period from the 6th to the 9th century, the Slavic tribes were divided into three main groups: Western Slavs, Eastern Slavs and Southern. For example, Western Slavs settled in central Europe. The Eastern Slavs occupied the territories of Eastern Europe from the Dniester River in the west to the Volga River in the east. The southern group of Slavs, in turn, settled in the northern regions of the Balkan Peninsula.