The "State Anthem of the Byelorussian SSR" was the regional anthem of the Byelorussian SSR, a republic of the Soviet Union. It was used from 1955 to 1991.
It took 11 years to create lyrics for it, even producing a version that mentions then-Soviet... Wikipedia
Lyricist: Mikhas Klimkovich
Composer: Niescier Sakałoŭski