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