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The British example goes straight against what you are saying, because at the time of both world wars, and especially the first, the British had plenty of war experience. And not just the British, but every empire at the time had plenty of war experience, but the war did not go at all like most were expecting it to. For a modern example of that with the US, just look at the war in Vietnam and in Iraq.
But more importantly than all of this, you are working under the assumption that the US is being led by extremely qualified people, and that every soldier would fall in line; however not only has the current US government been firing extremely qualified top officials because of “DEI”, but I doubt everyone in the military would happily invade a NATO member - with whom they’ve been allied and trained side by side for years - without even blinking an eye. Military experience does nothing to prevent a civil war, because one thing has nothing to do with the other. The military is made up of people too, who like I said before are a lot more connected with the rest of the world than they used to be.
Finally, even if it’s true that the US would somehow be immune to a civil war, that would still not mean the majority of countries would not fall into a civil war. To give just one example, Germany has a very big nazi far-right party that has been directly supported by Musk and Vance; if Germany went to war with the US, those people might take up arms against their own country.
Sean Lock had a similar thought.
He suggested calling it “Nazi Island”, but as one commenter mentioned “Isle Hitler” is probably a better name.