>By the late 1920s the economy of the United States had made exceptional gains in productivity due to electrification, which was a critical factor in mass production. Horses and mules had been replaced by motorcars, trucks and tractors. One-sixth to one-quarter of farmland previously devoted to feeding horses and mules was freed up, contributing to a surplus in farm produce. Although nominal and real wages had increased, they did not keep up with the productivity gains. As a result, the ability to produce exceeded market demand, a condition that was variously termed overproduction and underconsumption.