The phrase “breadbasket” as an economic term is as old as the references to Egypt as the “breadbasket” to Rome we see in the works of the ancient historians and many thereafter. It’s on the “A” list of overused historical metaphors.
There are even scholars who think that the South finally gave up because of this. The lack of food broke their back so to speak. Hungry, disease ridden soldiers aren't exactly gung-ho. No matter what the cause they are fighting for.