To start with the basics, armies aren 't the only organizations that run on their stomachs. So do civilizations. Agribusiness is totally dependent upon large machines and artificial fertilizers and pesticides in order to raise, harvest, and transport the vast quantities of grain, fruit, and vegetables we enjoy today. Fertilizers and pesticides require oil and natural gas, not only in their distribution, but in their manufacture as well. Also, feed for beef cattle, chickens, and turkeys depends very heavily on these same fertilizers and pesticides. When cheap sources of oil and gas are not readily available, the chemical industry passes the increased costs on to agriculture. The increasing prices for fertilizers and pesticides then results in increased food prices for the rest of us.
We may find ourselves eating farther down the food chain in the near future. In other words, we eat the grain instead of feeding it to something else first, since each link added in the food chain results in energy loss. In the future, the turkey and chicken "factories" we have now may not exist. The vast feedlots where cattle are fattened on grain before being slaughtered and made into hamburger patties for the nation 's fast food restaurants may no longer be economical.