The majority of Eastern European countries were not part of the USSR. They were USSR's allies in the Warsaw Pact - in the same way that the Western European countries were USA's allies in NATO - but they were independent nations. I'm talking about countries such as Poland, The Czech Republic + Slovakia (Czechoslovakia), Hungary, the countries that were formerly Yugoslavia, etc.
> Former USSR countries are mostly unified by the same language, religion (or lack of) and culture.
Not true at all. I've been to both Russia and several other Eastern European countries, and I can guarantee you that even within the former USSR there were many different languages, ethnicities, and religions.
Nitpicking: Poland, Hungary, Czechoslovakia and other satelittes of USSR weren't really independent. Certainly not in same way that UK or France were allies of USA. Maybe Yugoslavia was independent, but others for sure not.
Moscow made all the decisions, elections were rigged, there were uprisings, etc, etc. I know you probably know that, but just in case.
Note that Yugoslavia was not part of the Warsaw Pact. It was aligned with USSR until 1948 when the Informbiro period started - i.e. the Tito-Stalin split.
> Former USSR countries are mostly unified by the same language, religion (or lack of) and culture.
Not true at all. I've been to both Russia and several other Eastern European countries, and I can guarantee you that even within the former USSR there were many different languages, ethnicities, and religions.