It was in the 70s that the US government moved from telling corn growers how much to grow, which kept prices high, to planting 'hedgerow to hedgerow' and the resultant subsidies ended up pushing the price farmers get, to below the cost of production ( they only make money on the government subsidy ).  The end result is, they push third world countries in to signing 'free' trade agreements where locals don't grow food, b/c they can't afford to compete with US subsidies, which means famine when the US has no corn to dump, as when they started using corn for ethanol.  Also, most of the crop in the US is not fit for human consumption, it's only fit for turning in to products like HFCS.  I've driven through the midwest and it's just corn growing as far as the eye can see....