Napoleon said that an army travels on its stomach. The French general believed in his adage so much that he once held a contest to improve food-preservation methods.

It probably would have made a great reality-TV show on a cooking channel.

Yet food in wartime is anything but entertaining. Feeding the troops is one of the great challenges of military leadership. Feeding civilians during war can be even tougher.

As we approach Memorial Day, it’s worth remembering that there isn’t much difference between food security and national security.

Or think of it this way: Food is the ultimate weapon of mass destruction.

Bullets and bombs killed nearly 20 million people during the Second World War. Famine and malnutrition killed at least as many, reports Lizzie Collingham in her comprehensive new book, “The Taste of War: World War II and the Battle for Food.”

“The impact of the war on food supplies was thus as deadly in its effect on the world population as military action,” she writes. The Nazis used starvation as a torture device, rationing just 184 calories per day to Polish Jews. In Bengal, 3 million Indians died from a man-made food shortage.

Even when the fighting ended, the trouble continued: The world’s supply of food had shrunk by 12 percent, and in some areas the losses were catastrophic. Millions of people struggled to subsist on less than half of what they had eaten in 1939, reports Collingham.

Only in the United States did ordinary people continue to eat well. “American soldiers and civilians alike consumed significantly more food than their allies or their enemies,” she writes. “Most Americans felt that they were fighting to preserve the American way of life and one of the most powerful symbols of this lifestyle came to be the abundance of American food.”

It’s an abundance that continues today. Farmers grow so much food that we’re able to export huge amounts of it to foreign buyers. On my Iowa farm, about one out of every three rows of corn will leave the country.

Yet even Americans can feel the pinch. I certainly did in 1968, when I was a Marine corporal in Vietnam.

My platoon was patrolling a mountainous area west of Da Nang. Choppers delivered our supplies. We were supposed to receive a new set of rations every three days. At least that was the plan.

A dense fog once prevented the pilots from finding us. After a couple of days, we were willing to do just about anything for a bite to eat. We were faint from fatigue and worried about staying alert in a wilderness full of enemies who wanted to kill us.

Around this time, I found a Seiko watch on the trail. I thought it was my lucky day. So I wound it up and slipped it on my wrist. It worked for about 20 minutes. Then it stopped. So I tried it again. Same thing.

That’s why it was abandoned on the trail: It didn’t work.

Soon we met a group of South Vietnamese soldiers. I offered the broken watch for a bag of rice. I just didn’t admit it was broken. They thought I was a dumb American–but I knew better, and my platoon bolted away as quickly as possible. I had tricked our allies out of their rice, and we had about 20 minutes to skedaddle.

Later we came across a small farm and I stole a banty rooster. I was the only farm kid in the platoon, so it was my job to wring its neck, pluck the feathers, and cube the meat. We boiled the bird and rice in my helmet.

If you’re expecting me to say that nothing ever tasted better, you’re wrong. The meat was rubbery and barely edible. Even worse was the guilt, which came later, after a chopper finally found us.

I’m embarrassed about what happened, but it did teach me that hunger can make us subhuman. When you’re ravenous, you’ll cheat people out of their food, lying and stealing to obtain it.

This is the thing to remember about food and conflict: When you are famished, you will do almost anything to feed yourself. And when your children are famished, you will do anything to feed them.

So as you’re grilling burgers on this Memorial Day, be thankful for the soldiers who died to protect us–as well as for the abundance that we’re able to enjoy in this time of (relative) peace.

Bill Horan grows corn, soybeans and other grains with his brother on a family farm based in North Central Iowa.  He served in the US Marine Corp in Vietnam.  Bill volunteers as a board member for Truth About Trade & Technology.