Why will there be runaway inflation in the famine described by the black horse?

Les explains that the black horse indicates famine, because the food supply must be rationed. His premise is that if the great production areas of the North American continent—such as the Great Grain Belt to the north or the citrus groves and vast food-producing areas of California—are knocked out, along with the great food production area of Russia, the Ukraine, the world's food supply is almost annihilated. The rest of the world suddenly finds itself with no food, and it becomes so limited that there is absolute famine. The language of the verse boils down to a worker, the average field worker, having to work a full day from sunup to sundown just to earn enough money to buy enough bread to work the next day. Les says this is going to be runaway inflation caused by a shortage of goods, with a tremendous decrease in the production of foodstuffs. He also notes that famine is accompanied by disease, as seen in Africa and Somalia, and that the fourth horse, the pale one, ties together with these.