as part of his research into belarusian history, he postulated the existence of belarusian nationality with its own history, distinct ethnographical features, rich folk culture, with belarusian language being heir of the speech of the krivichi and the dregovichs. he supported "colonisational theory" of emergence of state in belarus, and considered krivichi and dregovichs largely to be isolated from ancient rus' state and therefore evolving differently. dovnar-zapol'skiy also postulated the absence of ethnographical unity in ancient rus' state, with external political and military affairs being the only binding factors in it.