Seems to me that the difference today, as compared with all previous examples is that we're hitting a hard limit imposed by the wreck we've made of the planet. None of the other empires had to deal with diminished biodiversity, plasticized-and-pauperized lakes/rivers/oceans, soil nutrient and microbiota depetion and other macrosystem factors whose impact is genuiunely not predictable because our knowledge is fragmentary and the macro system's an integrated whole that regularly demonstrates emergent properties. Sure, we have supercomputers spitting out models, but those are simply measures of uncertainty. There is, in contrast very little uncetrtainty about the insanity of continuing to pursue growth on a finite planet.

Do I know the upshot? Of course not. But can it be ignored as a precipitating factor within a US empire whose military escapades and anti-ecological corporate intrusions provoke environmental damage along with the obvious ill will causing countries to ditch the dollar and seek alternate economic buddies. Lots more natural-system factors operating that previous empires didn't have to confront.