I know a lot of Europe starved during world war 2 and America even sent ships of food over to Britian. I couldn't find anything on this sub or on google about it so I'm asking here.
Ok. here is a brief overview of American food production in World War II; read this to a slighter lesser extent backward for WW1. (I can expand if you want me to in a follow-up!)
World War II was a war of production, most of it American. Washington knew by 1938 “that any American involvement in another European war would be based on the strength of the United States economy and its potential for the production of military equipment, munitions, and logistical services”—well before the Lend-Lease Act of early 1941 cemented the primarily economic basis of America’s involvement. As Europe lost factories and farmland to the ravages of war, America produced enough goods to support the Allied forces in Europe, Asia, and the Pacific, as well as her own troops. In so doing, the American economy not only fully recovered from the Great Depression, but reached globally unprecedented heights; “The federal budget, about $9 billion in 1939, rose to $100 billion in 1945. Under that impact, the gross national product, 91 billion in 1939, reached 166 billion in 1945. During the war, 17 million new jobs were created, the index of industrial production rose 96 per cent, of transportation services 109 per cent”. Over half of the total world manufacturing production during World War II occurred in the United States. While the conversion of car factories to airplane assembly sites perhaps had a more dramatic effect on the popular mind, food was a vital component of this war by economic output. President Roosevelt even asserted in a speech to congress, “Food is as important as any other weapon in the successful prosecution of the war”. In fact, America broke food production records on their farms for three consecutive years in World War II (1941, 42, and 43). Rationing happened in World War II not because there was any shortage, but because the United States was committed to building itself into the bread-basket of the world, including both the Allied forces and the 'liberated' Axis lands, as tide began to turn with U.S. material and military aid. In the aftermath of the war, almost every country was deep in our debt, and food continued to be a crucial export after tanks, guns, and ammo were no longer necessary.
The flipside of exporting all our abundance of food is that World War II created the most intensely localized food economy the nation had experienced since the 19th century, and arguabley even before depending on all sorts of varying criteria. In 1943, close to 21 million families planted seven million acres of victory gardens across the United States. Life magazine reported with incredulity that “Every unprotected piece of ground was being dug up for victory gardens: in Boston's Copley Square and in the Portland (Ore.) Zoo, in Chicago's Arlington Racetrack and in the Wellesley College campus, in New York's Schwab estate and in the Naval Air Station at Olathe, Kan”. The phenomenon cut across class, race, and other demographic axes, reaching the White house and public housing alike: “Everybody was busy tucking seeds to bed in the moist spring soil—movie stars, soldiers, admirals, airline hostesses, nuns and prisoners”, the reporter noted. A National Opinion Research Center poll reported that 61 percent of Americans planned to have a victory garden in 1944—more than three-fifths of the population. Over the course of the war, those Americans and others planted more than fifty million registered victory gardens. Another NORC poll in 1944 found that 95 percent of Americans believed that victory gardens “helped increase the food supply last year”, and that 77 percent of Americans believed they “helped a lot”. The facts confirm popular sentiment: in the previous year, victory gardens produced 42 percent of the total fresh produce Americans consumed that year.
Sources:
The single most important book you should read about the US and other combatants' food supply is Elizabeth Collingham, The Taste of War: World War II and the Battle for Food, New York: Penguin Press, 2012. After that, I used:
EDIT: So much formatting help. Also, to get back to your bigger question, a specialist in the Civil War should talk about the EXTREME starvation and food supply issues in the South; there were instances of scorched-earth policy, while the embargo of the South didn't stop all shipments, but it stopped enough to have a significant effect. The levels of starvation experienced significantly helped in the deterioration of communications and trade of P.O.W.s; when the Confederacy couldn't feed its own soldiers, they weren't wasting any food on Union soldiers.