The first warning came from the Harvard Economic Society, an association of Harvard economics professors, early in 1929. The society predicted in its weekly newsletter that the seven-year-old expansion was coming to an end. Recession was ahead. Almost no one took the warning seriously. The economy, fueled by soaring investment, had experienced stunning growth. The 1920s had seen the emergence of many entirely new industries—automobiles, public power, home appliances, synthetic fabrics, radio,...