Another way to look at this is that, instead of assigning blame to one side or the other, we can view it as a historical inevitability. There were six empires during World War II: Japan, Germany, Britain, France, the US, and the Soviet Union. To a lesser degree, I suppose you could include Italy.
By the end of the war, Japan, Germany and Italy had been destroyed, conquered and occupied. France was struggling to recover from 5 years of occupation by Nazi Germany, and was near the end of their imperial era, while Great Britain, even though they were on the "winning" side, was broke.
That left the Soviet Union and the US to compete on the world stage and, coincidentally or not, these two nations also had opposite and competing ideologies as well.