Also the USSR made a buffer to the germans because they knew that the germans were going to start a war in europe, churchill himself admitted that those areas buffered against the germans were a strategic neccesity and also ideologically they’re polar opposites, you’re falling for western propaganda

they didn’t “collaborate to butcher the polish populace” they had a military parade because thats when they signed the molotov-ribbentrov pact of non aggression. The ussr actually invaded poland because they wanted to ethnically protect vulnerable ukrainian and belarussian people.