The Soviet union republic created on 31 March 1940 by merging the Karelian ASSR with most of the territory Finland ceded after the Winter War — a full union republic, transparently built as a shell for a future Soviet Finland.
Demoted back into the RSFSR as the Karelian ASSR on 16 July 1956.
The atlas holds 2 border frames for Karelo-Finnish Soviet Socialist Republic — the shape you scrub through changes in 1940 · 1944.
Verified scholarly history of Soviet Karelia, the region that became the KFSSR. (Open Library verified: Nick Baron, 2007/2009)
Verified standard English history of the Winter War whose settlement created the republic. (Open Library verified: Trotter, 1991)