A hundred years ago, 38% of Americans lived and worked on the farm; today, it is less than two percent. The impact of that change has been massive; the economist Joseph Stiglitz writes in Vanity Fair this month that the last Great Depression was caused by industrialization of agriculture, a "structural change in the real economy."
Agriculture had been a victim of its own success. In 1900, it took a large portion of the U.S. population to produce enough food for the country as a whole. Then came a revolution in agriculture that would gain pace throughout the century—better seeds, better fertilizer, better farming practices, along with widespread mechanization. Today, 2 percent of Americans produce more food than we can consume.