Formulation of the problem. Recently, issues related to the history of the implementation of the idea of Ukrainian unity have become extremely acute in ideological life. Along with statements about the absence of the phenomenon of the Ukrainian nation, denials of the fact of the existence of a full-fledged statehood of Ukraine, Russian politicians and some scientists are promoting misleading statements that the current Ukraine was the result of unfortunate mistakes of the leaders of the previous stages of social development, turned out to be a conglomerate of artificially "glued together" in the information space. a territory with an ethnically heterogeneous,or even simply predominantly non-Ukrainian, population. The purpose of the article is to highlight the chronologically first attempt at scientific and practical-political determination of the natural boundaries of territories with the predominance of the Ukrainian ethnographic element as an objective, fair, convincing criterion for their regular composition into a single national-state space. Using the methods of scientific objectivity, concrete-historical and analytical comparative research, the processes of ideological-theoretical and legal substantiation of the concepts of achieving Ukrainian unity in the times of the Ukrainian People's Republic, the times of the Central Council and the Directory, the Hetman's Ukrainian State and the Ukrainian Soviet Socialist Republic (1917-1920) are reproduced yr.). On the basis of the available documents and real facts, the picture of the implementation of interconnected concepts of the Ukrainian national-democratic revolution and the unification of the branches of Ukrainianism, which had been dispersed until then, is being reconstructed. A convincing conclusion is made that the observance of clear, principled guidelines for the ethnographic principle, as an unshakable legal basis for the formation of an independent cathedral state, brought undeniable practical results, while neglecting this principle, replacing it with other,mostly opportunistic approaches, ended without results. Key words: Ukrainian revolution, national unity, ethnographic principle, national territorial autonomy, independence, regionalism, separatism, Act of Zluka.