On 30 December 1922, Lenin and his aides formed the Soviet Union, by joining the Russian SFSR into a single state with the Byelorussian, Transcaucasian, and Ukrainian republics.[119] Eventually internal border changes and annexations during World War II created a union of 15 republics; the largest in size and population being the Russian SFSR, which dominated the union politically, culturally, and economically.[120]