The thing you always hear about our Great Depression = people were actually afraid of starving, they were going hungry etc. it is so obvious that there is one single very simple factor which causes everything. Farming. It is farming that tells you everything very very simply.
If farming is ok, so is everything else, if it isnt, so is nothing else isnt ok.
this is all you ever need to know - see eg Mayans, Easter Island whatever
Part of the starvation equation though, is that its more of an economic problem, than a lack of food. During the Great Depression, there was plenty of food around, but it couldn't be distributed because it cost more to ship it to market, than the stuff could be sold for. My family was potato farmers in Idaho in the 1930s, and they sold the farm and left after having to dump all their product at the rail stations because it had so little value. Interestingly, it worked out for me since they moved to Santa Barbara, and got into Real Estate. Many $$$ later, it was a good decision.
Back in the 1970s, it was all the liberal loons and Sierra Clubbers who promoted biofuel saying it would "save the earth" and stuff like that. Of course now, we see the economic side of the puzzle, which is that if you take farmland away from food production, food costs rise, and people starve.