When Complex societies collapse - as ours appears to be doing - they simplify.  Areas that supported hundreds of thousands or millions pre-collapse only support hundreds or thousands post-collapse.

Or none, as in the case of Chaco Canyon.

This is based on non-industrialized societies and we've only seen one system cascade collapse of an industrial society: The Great Depression.  

But we've never seen a cascade collapse with systematic multi-feedback loops, e.g., such as a collapse of global food production causing a collapse of raw resource extraction in Africa, etc., causing a collapse of First World manufacturing.  

The nearest I can come to it, others may be able to shed more light than I, was the collapse of the Celtic oppida in the Second and First BC.  In that time a relatively high degree of urbanization across Europe quickly collapsed, wrecking large scale manufacture (of fibulae, among other things), causing a localization of manufacturing and other economic activity.  They didn't lose their technology, per se, but they did lose the mass-market and other economic networks that made widespread, large scale, urbanization possible.  Towns still existed but they reverted to a lower scale of influence and depopulated.

Ever since I learnt about confirmation bias I've started seeing it everywhere