balance of power
After WW2 the US decides to adopt an isolationist policy.
No more involvement in Europe or Asian or even South American affairs.
I think first off, Soviets were reacting to our aggression, especially the bomb, yes the bomb did kill lots of Japs but we dropped it to show Russia what would happen, it was a diplomatic ploy, second, this is a situation you can't dictate who knows what would have happened without the polarity created by the cold war i dont think communist russia would have lasted that long, its amazing they lasted when they made the farms collective--we needed Russia to encourage exactly what Eisenhower warned us. 3-Power Vaccums are always filled, never has one country controlled all of the world's affairs--to reply to your situation which are absurd here we go
Using my imagination and seeding it with actual historic events I can see.
Communist Russia taking over all of Europe.
The only reason the Stalin wanted Poland and east countries was to have a buffer against the West, he was paranoid, thats why he partioned Poland with Hitler buffer zone. Second after what the 30,000 boys and old men did to the Soviets marching into Berlin do you really think they wanted to march into West Germany hun? The Russians could never truly defeat the Germans, in the modern era they have been the most effective machine known to man, and France(which is left leaning often but indepedent) would have been vicous, and the Brits would have been impossible to deal with and Franco's Spain would have got thrown into the mix-if your so right why the Commies not succeed in Italy and France? If you mean overt poltic means vs war. Besides with almost half of americans being german descent dont you think regardless what gov't policy is there are going to have tact support.
So number 1-Germany
Communist China taking over all of Asia. They can't even take away Taiwan, Japan would have taken over our role possibly with Australia's help and Korea's the Chinese Army was and still is shambles, a joke, flying 50's vintage fighter plains, lacking capital warships, if we hadn't stopped the Japanese from rebuilding their millitary (which is the second best funded in the world) do you think the Japanese would acqueise, so in some ways our intervention in Japan's affair (in your hypo we minus this 2) would prevented Commie China from hegemony, besides the Aussies wouldn't like it.
Communist Cuba taking over all of South America. How?
The powerhouses (army wise) of SA-Peru, Argentine Bolivia, Uruagary, now if Argentine cant defeat the antique tiny battlefleet sent by the queen to take the Falklands back Cuba is going 2?
Communist clients taking over all of the Middle-East.
No, they just bought weapons from the Soviets, hell we sold them 2, so did the French, the Israelis would probably for a profit. These areas if you haven't watched the news are Muslim. Thats the primary force dicating this, besidese the non-taken over states of Europe probably wouldnt dig it too much as Germany would be strong again and looking for a reason to Kick Russia's ass, because you can only kick France's ass so many times before it loses its charm.
Eventually there would be a Communist takeover in Canada and the United States.
How, dude you are crazy. I'm not even going to reply to last non a priori here. your off