Bret Devereaux's mental models

Their wordsIn order to move this army or sustain it in place it is thus necessary to ensure a massive and relatively continuous supply of food to the army. Failure to do that will result in the army falling apart long before it comes anywhere close to the enemy.

Their wordsThese small subsistence farmers generally seek to minimize risk, rather than maximize profits. After all, improving yields by 5% doesn’t mean much if everyone starves to death in the third year because of a tail-risk that wasn’t mitigated.

Their wordsNew land can be brought under cultivation (or cultivated more intensively) of course, but marginal gains decrease rapidly (because the best land is cultivated first and because adding more labor to already cultivated land, while it can increase harvests, is less efficient than cultivating new land) and there is a fairly hard ceiling on total production of this sort that was, for the most part, fairly low.

Their wordsAll of which is why simple graphs of things like ‘global historical GDP’ can be a bit deceptive: there’s a lot of particularity beneath the basic statistics of production because technologies are contingent and path dependent.