One thing about grains is that they can be stored almost indefinitely if kept dry, could be traded as a commodity and carried over from one season to the next in case of famine. The tubers not so much. Vast amounts of grain would create a more complex society than rotting potatoes.
Centralized grain storage provides a dietary equivalent of a water empire. Easy to defend, and easier for one small group to control.
American knowhow solved the problem
On a practical note, potatoes can be stored for months. I tried this last fall, as an experiment, and kept some for 5 months. They could have gone longer, I think.
Vast amounts of grain would create a more complex society than rotting potatoes.
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True enough but then you’d need pyramids to store all that grain.
It is also difficult to build an empire with an army sustained by a rapidly decaying food supply.
OTOH, the goose, deer & antelope, and bovine families don’t eat, trample, and make beds in growing potatoes.