Malcolm I do understand 20th European Century. In 1956 the Soviet Union and other Warsaw Pact sent troops into Hungary to put down an uprising and remove it's leadership, in 1968 they did the same thing to Czechoslovakia and in Poland well let's consider the list shall we
1. The Nazi-Soviet Pact
2. The Invasion of Eastern Poland and the subsequent terror that involved
3. The Katyn Forest Massacre
4. Allowing the Nazis to crush the Warsaw uprising
5. Imposing a communist government on Poland without the consent of the Polish people
As for Russian foreign policy imperatives well their clear they regard Eastern Europe as within their sphere of influence and they don't like the idea of nations within their sphere of influence acting independent like becoming Democracies or joining the EU or joining NATO. As for East Germany well here's what a former ambassador has to say on the subject.
https://www.friendsofeurope.org/insight ... largement/