Re: Karelia, this isn't quite as neat an example as the article makes you think: the vast majority of the native Finnish/Karelian population either migrated to Finland or died in Stalin's gulags, and was replaced by immigrants from elsewhere in the Soviet Union. According to the latest census (2010), under 10% of the current population identifies as "Karelian" or "Finn".
https://en.wikipedia.org/wiki/Republic_of_Karelia#Ethnic_gro...