[circlecity]

"Until relatively recent times, agriculture was not very viable unless you were in an rich delta or flood plain, which tend to be found near the coasts."

Well, there are plenty of inland river deltas and plains and agriculture is just as predominant inland as on the coast. We've had knowledge of fertilizer and crop rotation since the Old Testament. How recent the Old Testament times are in the scheme of events we are talking about here is, I guess, a matter of debate.

[Farmer Dean]

There is a lot of land that’s just unsuitable for growing crops.Most of that ground is excellent for grazing cattle.

[Boogieman]

“Well, there are plenty of inland river deltas and plains and agriculture is just as predominant inland as on the coast.”

Inland flood plains are usually narrower, and don’t offer as much land area for farming, which is why all the major ancient civilizations that developed agriculture were centered around deltas and flood plains near coasts (India, China, Mesopotamia, Egypt).

“We’ve had knowledge of fertilizer and crop rotation since the Old Testament.”

Rudimentary knowledge perhaps, but not the kind of knowledge we have today. Just throwing manure on stuff is not enough to compensate for depletion of a specific mineral, unless the manure happens to be rich in that mineral. Changing crops by season was done, yes, but it was done because different crops grew better in different seasons, not because we had systematic knowledge of which crops depleted which minerals, and how to counteract that by using crop rotation.