Well, as others have covered, the us has engaged in imperialism directly, in the past, and indirectly even now.

But I don't think that answers your question.

The "modern" US, and I use the word modern to represent the post ww2 era, has a very different place on the world stage than it did before ww2, though that place started shifting after the first world war.

You simply can't ignore ww2 and the effects it had on global politics any time something like this comes up. Most of what we think of as the way things work go back to that time even more than the nations' individual histories. There really wasn't any nation that wasn't deeply and radically changed by that.

After ww2, there was a global desire for peace and stability, with stability being the greater goal. The UN, NATO, all the major alliances and blocs stem from that.

Nukes played a huge role in major nations not being willing to just go out and conquer. It forced everyone to play a bit less overtly, so we ended up with proxy wars and coups and other fuckery when world powers wanted to extend their influence.

But, there's also another big factor. You go out and conquer somewhere, you have to manage it. You take over Columbia, you now have to run Columbia, protect your ownership of it, and deal with the people there being your people. That's a heavy burden for a world power. It's one thing to maintain a small island as a territory (think Guam as an example); it's a whole nuther thing to try and take over a nation that not only isn't going to be done without worldwide resistance, but is harder to maintain control over because it isn't contiguous.

The U.S. has a pretty major advantage by stretching across the entire continent. We've got entire oceans as borders, and entire nations that also stretch across the continent as neighbors. It's a nation that's damn near impossible to invade, blockade, or otherwise use direct methods against. Why would a nation give up those advantages by taking over somewhere else?

It's way easier to use other methods to control other nations rather than own them. Fund groups inside the country that are friendly to your nation, let them take over the country, and profit (literally, since there's a long history of the U.S. interfering with other countries' governments for nothing other than capitalist gain).

If the other country doesn't have an economic value, but have strategic positioning, or can serve as a puppet state or as a distraction, it's still easier to just stage a coup, rebellion, or otherwise put the country in a condition that's better aligned. It isn't and wasn't just the US engaging in this kind of activity, but the U.S. was pretty dominant on the western side of such activity. Our allied nations backed those plays, but the U.S. often called the shots.

In other words, the U.S. has never wanted or needed to conquer anywhere else after ww2. There were better ways to achieve goals.