Re: The abrupt start of the Cold War
I think it is not inappropriate, to point out that the whole genesis of World War II was to drive an appeased Hitler East against Russia. https://www.marxists.org/archive/bland/1990/x01/german-soviet-non-aggression-pact-1939.pdf
or if this is too un-palatable to read or digest, perhaps people feel more comfortable with Geoffrey Roberts (Emeritus Prof Cork University; 'Stalin's Wars: From World War to Cold War 1939-1953'; Yale UP New Haven & London 2008; still in print & easily available).
This on-going refusal to acknowledge what was happening in the buildup to WW2, remains a remarkable myopia on the part of many leftists. No doubt it is quite inconvenient to a cookie-cutter view of the USSR. However, it is not as if the Cold War was anything other than a continuation of the 'Hot War'.