One response to the OP is that the term “empire” simply doesn’t apply, unless you use a very loose definition of the term which would probably apply to almost any nation on earth.

I believe it's all political propoganda really, and an attempt to bring people towards patriotism of their country, because to be honest, most Americans (again I am an American) do not have any sense of obligation/responsibility to their country or others, it's all about entitlement and self. And really most people have more loyalty to their state then the US as a whole

I'm a US citizen and am currently in AP US history so I've recently learned about America's "Experiment in Imperialism"
Basically, America never reaally had colonies, they were called protectorates, countries the US would help set up and would leave when their governments functioned better (ex Philippines). They intervened in governments under different policies like the Roosevelt collorary, but only mainly used these countries as economic resources. the term colony was almost never applied. Also this wasn't a big period of time and no Americans really moved to these countries/spread an influence other than that of industry.
For these reasons and the reason that why would the US make this a significant part of everyones knowledge if to the country it didn't have THAT big of an effect is why i think many US citizens don't know about the US's experiment in imperialism.

Some of this still sounds very much like a colony but I think the difference is that for the European nations that went thru the Imperial Period as you describe they directly set out with the intention of establishing that colony. The territories currently controlled by the US were generally acquired either during military conflicts around the time of its independence....
The leaders of the US territories are directly elected by their population and I believe they have established their own constitution as well.
There was not a period in US history where it actively sought to acquire lands from another political entity and set up its own colonial governing body anywhere close to the dramatic expansion of the European nations during the peak in the 1500-1800s.

Was Manifest Destiny imperialistic? Yes. But imperialism is most obvious as the forceful military subversion of a sovereign state, rather than any grasp at territory that isn't yours.

Both areas are occupied--the difference is what they're occupied by. It's still imperialism. But the US participating in the inter-tribal warfare of the Plains Indians is somewhat different than sneakily subverting the government of Cuba. Just my opinion.

I did learn about imperialism is school, but I do think it was downplayed. I think American historiography also has a lot to do with the way Americans view the US empire. Re-branding the conflict between Cuba and Spain the "Spanish-American War" says a lot. Additionally, like I said, the Europeans were much more obvious about their intentions to establish empires, based on my studies. Imperialism in the US was often accompanied by progressive values.

The specific example I was thinking of was what I mentioned earlier--European nations had a council to divide Africa to specifically further their empires, whereas in America, the support for the war in Cuba, the movement west, etc, were specifically (popularly) promoted by an interest in addressing "people's well being" as opposed to just conquest.

The motives may have been slightly different, but they were still misplaced. It's White Man's Burden. I know that concept originated in Britain but I'm not sure how much it permeated European thought. If you take a look at the painting "American Progress," you can see a good example of how American empire-building looked in the western US. American settlers pushed forth, with or without the help of their government, to bring the American way of life to the Natives. A key here is Christianity as well.

So what I'm trying to say is that both the Americans and Europeans thought that they were bringing liberty to the world through conquest.

I can get behind that and I don't really think we're actually arguing anything. I wasn't sure if there was a difference or not.

With the Monroe Doctrine, the US expressed that Europe was not entitled to expand in the New World. Of course, the implication there was that the US was the one entitled to conquer the New World, though they didn't act on that nearly as much as they could have. Likewise, the US was invited to participate in the division of Africa but declined. The US was not as concerned as Europe as expanding their empire or competing with others to do so.

That might well have been the case because there wasn't much competition in the New World. For example, I mentioned that if Spain wouldn't have Cuba, the US would. There wasn't a great impetus to conquer.

That was the propaganda, anyway, and how the average person rationalized being part of it. I guess blankets infested with smallpox bring their own kind of "liberty".

I think we have come to an agreement on the matter then. So going back to my original question, why do you think many Americans do not even consider the United States as an empire before WWII. The US was not as transparent about it as Europeans but as we have discussed the evidence is all there. I don't mean for this to sound rhetorical but do you believe that the reason is simply because the US was not transparent about their 'empire building?' Or do you believe there are other reasons.

I found a very interesting discussion a while back that showed reports of the first colonial visitors to the eastern coast of North America that encountered very large populations of natives. There were obviously fairly large gaps between those visits and the more establish colonial settlements. As future visitors arrived the native populations were already much smaller and in some areas continued to decline.

That was the propaganda, anyway, and how the average person rationalized being part of it. I guess blankets infested with smallpox bring their own kind of "liberty".

...that the first European visitors brought smallpox that devasted 90% of the native populations. The premise is that native populations were upwards of 25 million in NA alone, and the "bounteous nature" witnessed by early explorers (think Lewis and Clarke) was an ecology on the rebound from widespread native control by fire that had not yet reached an equilibrium.