Between 1919 and 1920, the eastern territories of the former Polish-Lithuanian Commonwealth were temporarily administered by the Civic Management of Eastern Territories, established by Józef Piłsudski. The residents of the former Grand Duchy of Lithuania were to determine their future governance. Piłsudski placed the Civic Management outside the structures of the Polish government, while his opponents from the Polish nationalist wing wanted to suborn it to the government in Warsaw. Based on hitherto unknown archival documents, the author describes the reasons for the failure of Piłsudski’s federation idea, both on the Polish side, as well as errors by Belarusian leaders and the policy of the Lithuanian state.