When countries go into full mobilization for war, young men are now in the armed forces instead of working on farms or in factories. Even those not in the armed forces are needed for work in industries tied to war goods. Certain things like agricultural chemicals can be in short supply, or materials to make new farm equipment. Add to that the destructive force of bombing or attacks on transportation routes -- the connection is severed between urban centers and rural food production. So, one area of the country can have an abundant food supply, but if there is no transportation to other regions, they can suffer famine. And when the opposition takes control of an area, they usually funnel those goods (if they're not destroyed) into their supply chain. Another factor is that people may hoard goods during wartime, either fearing deprivation or to wait for an increase in price, which causes scarcity and increase in prices. ED: I want to add that many countries import foodstuffs. Wars can cut off international trade.