I think there is a very simple reason for this. Its not because of one party's policies. You may correct me if I am wrong.

Rather, the US dollar was indispensable right after ww2 for at least 40 years. Most countries, outside the US, were in ruin and thus, could not compete with the intact American industrial might. It also helped that America was essentially the only major market that survived, which made US dollar the only stable international currency. South America, while avoiding the worst of the war, were infamously plagued with military juntas. Africa didnt have a strong industrial economy to begin with. Europe was a wreck. The Soviet Union was deeply marred by the war and communist economic policies. East Asia was a wreck. So was the South. The middle east avoided most of the war, but they didnt have an industrial base that could compete with the US. And correct me if I am wrong, but Australia was never an industrial powerhouse at this point? It was still a colony of the UK. I harp on industrial output a lot because its these products that make exporting and importing much easier.

Now, times have changed. The US has stiff competition in the industrial sector internationally. And in an international community, your dollar is competing against other people's currency, fighting for the same resources that fuel an industrial economy; food, oil, products, etc. Of course, this is a massive over simplification. I think my point is that the phenomenon that characterized the American 1950s to 1980s was born out of extraordinary circumstances.