The British didn't really make unforced errors like Germany did, though. They mostly were forced into a fire sale situation as they were fighting for their lives. Even with everything they sold off, they were still within an inch of surrendering. The French story is similar. They may have been in a slow decline, but the war threw them off a cliff.
It's hard to look at what the US is doing and not become extremely angry, because historically the dumb hubristic nationalism always leads to crushing misery. It's so utterly predictable, and yet we're forced to watch the idiocy play itself out again.
I agree but the difference between the French and the British is the French really didn't have a choice (they got physically invaded).
You could make a very good case that for Britain entering into WW1 was a catastrophic and ultimately unnecessary decision. And you could make a (much more controversial but I think also true) case that entering into WW2 was also not necessary and ultimately fairly catastrophic.
Yet the British elites chose to do both. Pride, hubris, stupidity, maybe well deserved, call it what you want, but in the end British power was given away cheaply. I think what the US is currently doing is foolish but as you say there's also a sort of inevitability about it.
Edit: You could also add the Soviet Union to this, an even more recent example of the end of an empire. Towards the end during the Gorbachev era policymaking went from relatively "normal" (by Soviet standards) to extremely bizarre in a short space of time
When societies can't solve their internal problems internally they tend to turn outward for solutions.
Everybody could see the long string of preventable phenomena leading up to this: financial deregulation, decline of civic institutions, high levels of deaths of despair, rampant individualism, unchecked commerce, rising internal violence, rising inequality, rotten media landscape, open political corruption (not in this order).
My only hope at this point is the minimization of violence when the US resets.