The United States found itself with an extraordinary empire, which it also intended to abandon. This was a genuine wish and not mere propaganda. First, the United States was the first anti-imperial project in modernity. It opposed empire in principle. More important, this empire was a drain on American resources and not a source of wealth. World War II had shattered both Japan and Western Europe. The United States gained little or no economic advantage in holding on to these countries. Finally, the United States ended World War II largely untouched by war and as perhaps one of the few countries that profited from it. The money was to be made in the United States, not in the empire. The troops and the generals wanted to go home.
But keep in mind that it rests on a definition of "empire" that includes a grouping that we didn't want, which didn't benefit us financially, and which we didn't try to actually own.
So if you use the tighter definition of a grouping that is conquered, held in place by power, and exploited for money or resources to condemn America for being an "empire," think again (or just once, really).
Which isn't to say that we don't benefit from the system we have built since World War II. So we should defend it.
But I have trouble calling what we built an "empire" given the baggage the term carries with it.
And while I have no problem with the idea that we have to focus on our interests and that thinking of our strategy in imperial terms can be appropriate, I have trouble with the notion that balancing between friends and nutball foes rather than helping friends balance foes is the proper way to maintain our interests.