The purpose of the research paper is to study the views of the famous figure of the Ukrainian diaspora, historian and publicist Roman Brzeski on the reasons for the defeat of the Ukrainian Revolution of 1917-1921. Scientific novelty. Roman Brzeski's understanding of the reasons for the defeat of the Ukrainian Revolution of 1917-1921 and the impact of that defeat on the further development of Ukraine is shown. The research works of R. Brzeski, memoirs, and theoretical texts that have not yet been the subject of historical analysis are used. Conclusions. Roman Brzeski was a follower of the ideologues of Ukrainian nationalism Mykola Mikhnovskyi and Dmytro Dontsov. His analysis of the reasons for the defeat of the Ukrainian Revolution and each of the national governments that operated in 1917-1921 - the Ukrainian Central Rada, the Hetmanate of Skoropadskyi, and the Directorate of the Ukrainian People's Republic - radically contradicted the views of most of the heads of those governments on that problem. The main reason for that was the political antagonism between the independentist R. Brzeski and the majority of that time Ukrainian political establishment. In his memoirs and historical and publicistic works, R. Brzeski sought to prove that Ukraine had the necessary objective prerequisites for transformation into an independent, successful European state and that the Ukrainian people aspired to it. The tragedy of the Ukrainian Revolution, in his opinion, was that it was led by people who did not think about the future of Ukraine as a European fully sovereign state, independent from Russia in the economic, political, social, and cultural sense. R. Brzeski was convinced that the Russian political class and Russian society would not agree to any concessions to the Ukrainian movement. The categorical rhetoric and accusatory tone of the author's statements, which were combined with accurate assessments of the causes of events, personalities, and political processes, were a characteristic feature of his reflections.