“But a man-made non-nuclear event? We’ve been there, got T-shirts. The ones of us who’s ancestors survived.”
Can you give an example of a 90% die-off in one year across a major nation of 100s of millions of people?
The worst die-off humans have had, outside of the weather change about 14,000 BC when we had the genetic bottleneck, was about 50% during the black death.
The high tech Roman society died with fewer casualties, but greater loss of technology. Lost were clean water, running water, hot water, baths, concrete, correctly designed roads, surveying, engineering mathematics, and a host of other things.
History was replete with examples of that being clawed back.
Our high-tech world also changes the equation.
We don't have to mine for materials.
Any metal you want to name (leaving out heavy nuclear elements), from aluminum to zinc is available in any crappy burned out car.
In pretty pure form, without a lot of effort or technology.
Collapse is much more complex and much less linear to predict than one would suppose.
/johnny