Let's follow up in detail on the post about the most convincing argument against interventionism being that we are no longer capable of imposing our will on other societies and enjoying the spoils of war. First, we'll look at the long phase of our successes in imposing our will, through WWII, and the next post will go into the long phase of our inability to impose our will.
All empires begin with a seeming invincibility -- gobbling up more and more territory, bringing more and more subjects under their rule, and enjoying more and more spoils of conquest, whether material or strategic / geopolitical. Nothing succeeds like success, drawing out one victory into an extended stage of expansion. We don't need to go into what makes some particular society start to grow into an empire, rather than some other society (see Peter Turchin).
In American history, this began almost right after we landed in the New World, as the Indian tribes attacked us and made us band together in collective self-defense. With that collective solidarity, we were then able to expand further and further at their expense -- the cohesive will destroy the fragmented. We then grew at the expense of our British homeland, then the French, then the Spanish, then the Mexican, and all along still against the various Indian tribes we encountered. That takes us up to the closing of the Frontier around 1890.
But even after that, we kept expanding and expanding, beginning with the Spanish-American War in 1898, which extended our sphere of influence into the Caribbean and the South Pacific, followed by a series of invasions and interventions throughout Central America and the Caribbean, most notably to secure the Panama Canal. Lasting from the turn of the 20th century through the 1930s, this stage has been referred to as the Banana Wars.
Our final event of successful intervention was subduing Japan during WWII, using the mother of all intervention tactics -- dropping nuclear bombs on two of their cities. That more or less rounded out our growing sphere in the Pacific, against the Chinese sphere.
What characterized these successful interventions, as compared to our inability afterward?
Whether or not we colonized the land with our own people, we added more territory and people to our sphere of influence (rather than them remaining truly independent or under another nation's sphere).
We left their material way of life more or less the same, so that our new territory could continue to provide us with spoils for the indefinite future. No use killing the goose that laid the golden egg, whether that's sugar, oil, or whatever else. More for us, less for them -- but not destroying their economy.
And we brought about stability as soon as possible after defeating them, in order to get those spoils flowing as quickly and as trouble-free as possible. The only difference was that now the stable order was presided over by a leader of our choosing, not of their own.
The spoils did not have to be a cash cow kind of thing, it could have been a strategic defense position against encroachments by other strong nations. Still, that required us to incorporate them into our sphere of influence, leave their livelihoods more or less alone, and maintain law-and-order. What good is a defense outpost that cannot support its inhabitants and that is subject to turmoil? That would hardly make a solid block against incursions.
Or it could be a relatively unchanged society that becomes a client state or strategic ally after we make them a geopolitical offer they can't refuse (like Japan).
A simple test is to see whether the territory we targeted ended up looking like and serving like just another state of the Union, even if the residents did not get citizenship. As we acquired more and more territory within what is now our current borders, we did not destroy the land or leave it in a backward state of chaos. At most we removed the inhabitants if we were colonizing the land, but did not wreck it otherwise -- we wanted that new land to support our way of life and possibly even feed further expansion.
Crucially, none of these places that we absorbed into our sphere of influence did so willingly, proving that (once upon a time) we were in fact capable of imposing our will by force. They did not ask us for incorporation, and we did not use mutually beneficial negotiations. We used force to defeat them and then took them over for our own benefit. They figured it was not worth it to revolt and get defeated all over again. If they did revolt against, say, our local puppet, we either suppressed the rebellion or installed someone else who was more to their liking, but still our puppet.
Next we will look into the history of failure in imposing our will in order to enjoy spoils, which began right after WWII, as we tried to incorporate the Korean peninsula into our sphere of influence (against the Chinese sphere), but only ended up getting half of it, and leaving the war in a stalemate that continues to today.