Isolationalist is not the opposite of imperialistic. America was imperialistic without being involved in the greater cares of the world. Refusing to get involved in the Napoleonic Wars for instance.
Agreed, agreed, agreed!
And imperialistic doesn't include things like the Louisiana Purchase. Buying the right to purchase land from, and negotiate treaties with, the natives of an area is not imperialistic. Going on and having wars against those natives is.
Strongly disagreed!
We USAians are strongly, from our origins, fundamentally imperialist. The Louisiana Purchase was brilliantly imperialist--that we could get that vast acquisition without firing a shot (shots were fired later, in the War of 1812, to confirm our claim to it) was a fantastic coup. But it was an imperialist transaction, I cannot see how there can be any doubt of it. What after all was
Napoleon's claim to this territory? What right did he have to sell it? Arguing that it wasn't an imperialist acquisition is like arguing that a man is not a slaver if he didn't capture all his slaves from their homes himself, but "only" purchased slaves from a dealer offering to sell them.
English speaking America exists entirely as an exercise in imperialism on the grandest scale.
Your point about the question of entangling alliances with other imperialist powers being irrelevant to the determination of one power being imperialist or not is very well taken, and undermines the distinction you wish to make.
Now then, if the USA had ever expanded because an established nation not stemming from an invasion of US emigrants dominating other peoples who had lived there before or came in as alternates not mixed in with the USAians, developed a strong majority sentiment for joining our Union, and negotiated such incorporation on their own behalf, I would agree that would not be an instance of imperialism. Let us say the people of Chile all decided, or anyway an overwhelming democratic majority of them, like 70 percent or so, that they wanted to be in the USA, and we agreed we wanted them to, and by treaty it was incorporated and a number of states of the Union with representatives and Senators elected by the Chileans went to Washington, and native born Chileans became as eligible as anyone born in the older USA to be elected President and so forth, then that in itself would not be imperialist. (It would be ASB as all hell of course!) Imperialism could be involved--say this happened in the late 19th century, and one reason Chlle wanted into the Union was to be able to have deep backing for a venture to conquer all the niter mines in the region to the north, and one reason the Anglo-Americans agreed to take in a bunch of Spanish-speaking South Americans was anticipation of that niter monopoly (not to be had without war with Britain of course...) that part would be nakedly imperialist. But not the incorporation, if it were desired by a legitimate majority of Chileans, for whatever reason.
Ah, then, what about Texas and California? Well, you might as well mention Hawaii in the same breath. In all of these cases, governments were formed, by emigrant US citizens, that petitioned for admission to the Union. The difference versus my ASB Chilean scenario is--these states were formed by a wave of invading Americans, who overrode the interests and rights of people who had been living there before. In Texas and California the numerical majority of these were other imperialists, Mexicans settling there mainly to secure Mexico's claim, the Californian project going back to pre-revolutionary days under the aegis of New Spain. To a degree, non-Anglo Tejanos and Californios did ally with the invading Anglos to support independence from Mexico, but in retrospect they were obviously and blatantly betrayed. Meanwhile a whole lot of Native Americans were having their very humanity, let alone political and civil rights, pretty much ignored and trampled upon. (That some of these were not themselves very nice people and might even be called imperialistic themselves does nothing to negate the fact they were taken advantage of). Hawaii of course most people would agree right away was a plain instance of imperialism--yet the terms on which Hawaii came to be incorporated were essentially similar to the process in the earlier continental cases.
Alaska was acquired the same way Louisiana was, in a friendly deal with a fellow imperial power with both partners to the deal treating the Natives like so much commodity cordwood, the Russians having accomplished dominion over the natives by a combination of trade, missionaries--and brute force from time to time. Clearly imperialist. Clearly imperialist to purchase it without bothering to talk to the people who lived there and ascertain their desires. The Southwest and Florida were nominally purchased, from Mexico and Spain. I've never seen an evaluation of how much the money paid for the conquests would appear to have been a fair compensation, but even if it were such, the deal was still forced, with guns to the heads of both "freely" selling party. Clearly imperialist.
In fact there are no parts of the USA that were not conquered at some point or other, by the people we claim cultural descent from.
We are all about empire.
It really isn't until after the Civil War you get the US caring to butt it's nose into other nation's affairs that would not otherwise be in it's self-interest. Attempting to annex Dominican Republic is imperialistic, but the US is still isolationist. Roosevelt arbitrating the end of the Russo Japanese War is not imperialistic; but does show that he took the US out of isolationism (for the time being); while the Boxer Rebellion is an example of the US being imperialistic AND not being isolationist by cooperating with other Western powers.
All sensible.
Perhaps you can offer a rigorous definition of imperialism in the relevant context of the 19th century that does let the USA off the hook? I suspect if you can do it though it would let off lots of other powers normally accepted to have been imperialistic, like say Russia for instance. Or completely rob the term of all useful meaning.