Not to get weighed down in pedantry, but the Wikipedia article is “American imperialism”, not “the American empire”. Taking imperialist actions is a low bar for determining what is or what is not an empire. I wouldn’t call Yugoslavia an empire, as an example. Even the USSR is tough to call an empire, for some reason. Maybe because it collapsed so quickly.

Now that I peruse a bit, I guess scholars use the term “imperial power” to get away from the colloquial baggage of the term “empire”.