Before tractors, farmers worked their fields by relying on their own strength -- or that of oxen, horses and mules. The advent of the first portable steam engines ushered farming into the modern age.
By the 1870s, self-propelled steam engines were being used in America's heartland to help harvest wheat. These steam engines -- the forerunner of the modern tractor -- towed threshing machines from field to field where farmers used the behemoths to separate grain from straw and debris.
By the 1920s, tractors became light and versatile enough to work the fields. In 1924, the Farmall tractor became one of the first general purpose machines to pull harvesters and a variety of other equipment to plant and cultivate crops. Within a decade, 200 Farmalls were being built each day to keep up with demand, and a host of other manufacturers (like John Deere) had introduced similar tractors. Suddenly, farmers could work more land faster with less help and produce greater yields [source: Moore].