It might be related to the gold standard, but I'd argue that WW2 was a bigger factor. The US was already the strongest economy and the competition was devastated by war. Add on to that the development of the intermodal shipping container and it was suddenly possible for the US to transport their goods cheaply. The reason this golden age ended is that other countries had finally recovered from the devastation of war.
This view totally ignores the domestic policies US took in the 60s which was bloated deficits from the new deal and Vietnam war which has been attributed to collapsing the Bretton Woods dollar system.
>How do other countries devastated by war have to do with US economic equality?
Because there was less competition on the international stage for the goods produced in the US. This meant that production companies could pay their workers more since they were earning more. Relatively low skilled labor would earn a lot more money. This lifted up the poor. Eventually those jobs started moving away from the US, because other countries could produce the same goods at lower cost since they could pay workers less.
>Shipping technology has only gotten better since than too but that just hurts mom&pops and helps online retailers.
None of it has been as revolutionary as the intermodal shipping container. Before that it took days and sometimes weeks to load cargo onto a ship. The main point with the shipping container is that it made international trade significantly cheaper.
The US could not have won the war without the wealth that still remained within the "fully backed" dollar even after all the shenanigans that had been pulled on the general citizens devaluing the dollar up to that point.
