Soviet republic proclaimed 1 January 1919, nominally independent satellite of the Russian SFSR until 1922, then a founding constituent republic of the USSR governing most of present-day Belarus.
Declared independence as the Republic of Belarus in 1991 as the USSR dissolved.
The atlas holds 4 border frames for Byelorussian Soviet Socialist Republic — the shape you scrub through changes in 1919 · 1939 · 1944 · 1945.
Standard scholarly history of Belarus covering the Soviet Byelorussian SSR period at length; used as a verified fallback since no dedicated BSSR-only monograph surfaced.