[bell-cot]

However "uncivilized" things often got, WWI and WWII were not collapses of civilization - even in 1945 Germany or Japan. Supply chains were dominated by American industry and the Allied Occupation Forces, but worked perfectly well.

Instead, look at modern-day failed states - lawless, unable to produce much beyond some subsistence farming outputs and lots of refugees (and angry, violent young men) - to get a sense of actual civilization collapse. If "government" in the US meant whichever well-armed local militia had won the last bloody fight, all 3 of the internet, electrical grid, and the petrochemical distribution systems were down - and there were no PLA occupation forces putting things back together - what would the recovery path look like?

And recall that the #1 test of "did that civilization collapse?" is whether the civilization's social/economic/governmental norms and structures lost legitimacy/authority in the minds of the (former) citizens. Outside of fantasy, you can't restore the 500AD ruins of the Roman Empire to its 140BC glory by hand-waving "now everyone just has to behave like we Romans did in the Good Old Days...".