One of the keys. Others are the USD as the defacto world reserve currency, the ability to project military might anywhere, and the US's ability to keep other countries from growing their militaries too much (making the other items in this list easier to manage). The US is quickly throwing all this away though.
While the USD is still the de facto reserve currency for some, many larger countries and blocks have made sure they are not reliant on it. Up to the point where weakening or strengthening the value of the dollar is far less than a power it used to be.
What happens when you "sanction" a significant portion of the world because they don't share your "values" or want to play ball elsewhere ? Well guess what ? These countries will inevitably look at each other and form their own trade routes and alliances.
Unfortunately, no hegemony is eternal.