Some nations of Europe have historically been a stumbling block for the advance of socialism. The Baltics, despite being liberated by the Soviets and allowed to retain their languages and identities, responded by sabotaging the Union and defecting to NATO.
Engels dealt with such entities by counting them as Volkerabfalle, or people which are counter-revolutionary by virtue of existence, and who should be absorbed by historically progressive cultures (in the case of the Baltics, Russian culture). I am inclined to agree, seeing their tendency towards fascism.
What do you think, comrades?
Entirely unscientific analysis. Completely ignores the existence of many devoted Baltic Bolsheviks, as well as the fact that they voluntarily joined the Union. The causes and dynamics of the nationalist-bourgeois counter-revolutions in the former Soviet republics and other eastern European former socialist states are complex and worth trying to understand but this ain't it chief.