A key thing about the mid-century is that the actual manufacturing capabilities of most of the world (with the sole exception of the US basically) were completed destroyed by WWII. Britain and Germany were devastated. This means that in the 1950's the US was essentially acting as the sole industrial power at full strength serving the rest of the world. We were playing worldwide economics on easy mode: as if we were the only ones that had modern technology and fully functioning infrastructure, while all other countries wanted our goods. This is why it is bizarre to draw any conclusions about taxes or any other economic principles from this very unique period of time: you could probably put in place just about any law and still have the United States be ridiculously successful. We are now actually competing with other parts of the world.