I think it was the entire productive capacity of the remaining world being bombed to destruction was the reason the USA experienced prosperity during that period. The US dollar becoming the international reserve currency probably helped also.
Just to clarify, I'm not trying to make the claim that the US was prosperous during that period solely because I think the war created more conscientious people. But I do think part of the reason you saw that prosperity distributed better and had things like pensions was because people back then had a better sense of what the cost of NOT distributing more fairly is, along with a better sense of the importance of camaraderie. That's an admittedly romantic view of the time, but I think there's truth to it. Widespread adoption of computers has lead to huge increases in prosperity after that period, and I think part of the reason that hasn't be shared is that the generations since then are more child like and have less of a sense of responsibility.