America's goal is to maintain their global hegemony. Their hegemony is in all domains, in economic, military and diplomatic.
Now, let's just take one domain for example. Let's say economic.
Check the IMF voting rights. China has less voting rights in the IMF than even France! Whereas the US has more than the other main players combined. Despite China being the largest trading power in the world, and the largest creditor nation in the world, we have less say in the IMF than France, Germany, Britain, etc. And America has more than all of those combined.
Now, another topic, the US dollar. The US dollar being the world's reserve currency (and the currency in which oil is priced) gives America what many have referred to as the "exorbitant privilege":
Exorbitant privilege - Wikipedia, the free encyclopedia
Why do you think America can print so much money all the time? With zero percent interest rates, and yet they are launching how many rounds of quantitative easing?
The reason is because the USD is the world's reserve currency, by using quantitative easing (money printing) they can push inflation into the developing world, and borrow money at absurdly low rates.
Obviously, the money that is printed does not come out of thin air. It comes out of our pockets, China/Japan and everyone else who holds USD as reserves (basically everyone). By printing money, they are devaluing the dollar, and thus devaluing our reserves, it is essentially a stealth tax on us.
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One main goal that China has, is to change the world's reserve currency from the USD to a more equitable "basket of currencies". This removes America's exorbitant privilege, and makes it easier for us to compete on the global stage, and prevent our reserves being willfully devalued and stealth taxed by QE.
Does this benefit America? No, in fact it will have massive costs on America, who will find their cost of borrowing soaring, at a time when they already have such a massive borrowing problem. Along with countless other problems that come from losing the reserve status of the USD, most of which will have a negative effect on American economic competitiveness.
America gains a lot from their global hegemony, not just in economic terms (as mentioned above), but in all areas, including military and diplomatic. If China becomes a developed country in the next few decades, that will put severe pressure on the American global hegemony, and remove some of the exorbitant privileges that they receive from currently being the world hegemon/leader.
Bear in mind that we have zero designs on becoming a world hegemon ourselves, even if that were possible (it's not), I believe the era of superpowers and global hegemons is over, or will be within the next few decades. Thus, a multi-polar world is better for us, a world in which America does not have an exorbitant privilege, which comes at the expense of our own competitiveness.
Apologies for the long post, usually I am not so long-winded.