The article is devoted to the new historical investigations on the idea of Constituent Assembly and the factor of the Lithuanian language usage area in the context of Baltic-Slavic-German historical neighbourhood. The State Council of Lithuania aspired to a large geographical space for the national statehood in 1918. A Constituent Assembly (Steigiamasis Seimas) was elected 1920 in the area where Lithuanian- speaking population dominated. Until 1990, Lithuanians comprised about 80 percent of the total population in the Soviet Lithuania, and, after the reestablishment of the independence, a zero variant of citizenship was accepted. From the historical perspective we can better understand the Lithuanian national strategy of the years 1918–1920, when the leading Lithuanian politicians revendicated the great territory with millions of Slavic-speaking population