THE INDUSTRIAL REVOLUTION began, in the 170Os, with the mechanization of the English textile industry, and gathered strength with the steam engine, the steamship, and the locomotive. It reached the farm with the reaper, which amounted to a large horsedrawn lawn mower that could cope with tall stands of wheat or grain, putting an end to the age-old practice of having a crowd of men advance across a field swinging sickles or scythes, followed by women and children who collected the cuttings.

McCormick was not the only inventor of a reaper, but his much-improved model qualified for a patent of its own, and in 1851, in Chicago, he built the world’s largest reaper factory and produced the machines for sale. He introduced innovations in selling, recruiting hundreds of local salesmen and placing them under the command of state agents, who received a commission on every reaper sold. He also pioneered in offering credit to farmers, who needed their new reapers in time for the harvest but could pay for them only after they had sold their crop.

During the last three harvests of the Civil War, McCormick sold some 160,000 reapers—85,000 in 1864 alone. The commissioner of agriculture declared that each machine had released five men for military service. Following the war, many of those now unnecessary farm workers found jobs in newly thriving factories. Thus McCormick’s reaper embodied a century-long trend: The mechanization of agriculture enabled fewer people to produce more food, thereby releasing a work force to build cities and run the industries in them, transforming America from a rural nation into an urban one.