Does the math.
Long range distribution of fresh food needs high speed. Distribution of anti famine food just needs to be cheap. Rome was fed by slow boat.
That's OK. The original premise is flawed. It's racist, among other things.
The USA has a rather large river running through the (rough) middle of it, which is useable for this sort of thing. The England before and as railways were built there was a fairly massive canal system built for the purpose of moving goods reliably and cheaply.That's hard to reproduce for societies without the Mediterranean just sitting there in front of them waiting to be turned into a distribution system.
Usable in some parts of the USA; the Mississippi is a HUGE advantage for rebuilding civilization in its basin as it connects a huge area and thus could support large cities even with 1500s tech. (Well, large by the standards of the 1500s). Which is why it was one of the urban civilization zones before the Little Ice Age threw the Cahokians down the stairs. (The other was the Ancient Pueboans in the Southwest, who also got thrown down the stairs by the Little Ice Age.)The USA has a rather large river running through the (rough) middle of it, which is useable for this sort of thing. The England before and as railways were built there was a fairly massive canal system built for the purpose of moving goods reliably and cheaply.
The point was that shipping grain around at 3 knots is totally reasonable; the issue is cost, not speed. A steam-electric hybrid truck or a horse-engine land barge at 6 MPH may seem to be crawling by modern auto standards but could be a huge win over oxcarts in both speed and fuel/food consumption. And if it doesn't work, the cost is likely the problem, not the speed. (It's hard to freight food if doing so consumes more food than you're freighting -- thus why land freight was historically expensive.) For famine purposes, relief food needs to arrive no earlier than the failed harvest, and you probably have a good deal of warning on that.That's hard to reproduce for societies without the Mediterranean just sitting there in front of them waiting to be turned into a distribution system.
I first came across this concept in Pastwatch: The Redemption of Christopher Columbus. I suppose a good way to recycle rusted iron is important.I've been told that most of the minerals, precious metals, and fossil fuels have been mined out of the parts of the Earth's crust that a pre-technological society could access, which is why we're doing things like deep-sea drilling, shale sands and so forth. This is to say nothing about the biodiversity we're losing at a chilling rate.
What we have here, now, is kinda our one shot. The only way out is through: we gotta keep going, because if it all falls apart, there's nothing left for the survivors to rebuild with, at least for the next couple million years.
Recycling rusted iron is easier than digging new ore and trying to purify it, because there's nothing in it that you don't want except oxygen. If you can get a hot enough fuel, charcoal being the best bet, to turn it back into liquid then you've got all the iron/steel you need. Said fuel is the major choke point for this, and you have to have enough of it to work through the various issues you'll encounter. If you don't have wood to turn to charcoal, or don't know you can or should turn it into charcoal for a hotter fire, then sufficient amounts of most hydrocarbon fuels will do.I suppose a good way to recycle rusted iron is important.