Estonia comprises, more or less, OTL Estonia.
In June 16, 1940, the Soviet Union invaded Estonia and replaced the leadership. Under the occupation Estonia voluntarily joined the Soviet Union.
Estonia was occupied by the Finnish army in the winter of 1941–42. The Estonians received the British-supported Finnish troops as liberators. Pre-Soviet institutions were restored and Estonia joined the Allies. This was a clear contrast with the other Baltic republics who went from the Soviet occupation to an occupation by the Third Reich.
Estonia made an important contribution in the war against the Soviet Union, and then as an ally stronghold during the cold war, even if Estonia never took direct action against the Axis. The liberation of Latvia and Lithuania in 1952 was, in a great deal, part of the Estonian position, backed by Britain and Finland.