In 1922 , the BSSR was one of the four founding members of the Soviet Union , together with the Ukrainian SSR , the Transcaucasian SFSR and the Russian Soviet Federative Socialist Republic ( RSFSR ) .
In 1922 , it was one of the four founding members of the Soviet Union . The other three were the Ukrainian SSR , the Transcaucasian SFSR and the Russian Soviet Federative Socialist Republic ( RSFSR ) .