We moved to a rules based world order, there is no imperialism after that, unless we want to return to a world of war (people forget how frequent this was before this, this is the reason the nations of the world agreed to the move, they didn't want to live in this terrible uncertain type of world). This world was also unproductive as people are too scared to take risks. A war economy isn't productive in the true sense as it doesn't improve the human condition.
A rules based world order needs someone to enforce those rules, with the US as hegemon, they ended up being the largest enforcer (in addition to the UN security council which has been neutered by China and Russia's moves to ignore it).
The benefit for the US is a prosperous, stable world. A consumer base with plenty of money to spend on US goods (the world economy is demand based), and a stable supply chain.