US being the engine of the world would not last long, the US dollar is already losing its relevance. Other country are beginning to abandon it as their currency of exchange. Without the US mingling in the affair of other countries and having a leverage, they would not have being the world power by now. Money doesn't flow towards the dollars technically but it flow towards the dominant currency which currently it's the US dollars but as I said it wouldn't last long. The US dollars is becoming a joke and so is their economy, the dollar isn't the strongest currency anymore as other currency are having more strength than the dollars but because the US is still the dominating country that's what is giving the dollar relevance.
I don't think the USD is losing relevance but just that some countries are trying to move away from using the USD as their reserves due to reasons best known to them while some countries are doing so due to the fact that the United States have placed sanctions on some countries from trading with the United States dollars. United States of America becoming the world power was due to their influence in the world economy and even till date they still maintain the world leading nation in economy according to the Forbes and even China that is rising very fast in their economy is no where close to USA.
Talking about United States mingling in the affairs of other countries that is basically because they are the world power and have the liberty to interfere in the affairs of other nations because those are some of the things that makes them superior to others. The United States dollars will continue to gain relevance in the international trade exchange market no matter how many countries decides to dump the dollars as their reserve currency but if any other currency will overcome the dollars they must first of all surpass the United States of America in terms of their economy and for now there's no country. As days goes by that's how the US is increasing in their intelligence and technology and these are the reasons why their economy keeps blooming.