I remind you that I asked 'Why?' in response to your bold statement "Not letting e.g. Baltics into NATO/EU would almost certainly mean they have been already absorbed back into Russia. The rest of CEE would be vassalized."
The only other recent aggressor was by that point completely pacified Germany.
Czechoslovaks, United Kingdom, France, Greece, Estonia, Serbia, Italy, Romania: https://en.wikipedia.org/wiki/Allied_intervention_in_the_Rus...
Germany, Romania, Hungary, Italy, Slovakia, Croatia, Finland: https://en.wikipedia.org/wiki/Eastern_Front_(World_War_II)
It was an invasion in support of one of the sides in Russian civil war. Russia made peace with Germany 1917 [0], the intervention started in 1918.
[0] https://en.wikipedia.org/wiki/Armistice_between_Russia_and_t...