In the years following the Civil War, the American economy underwent a transformation. Where once wealth had been measured in tangible assets—property, livestock, buildings—the economy now ran on money and the new devices of business—paper currency, securities, and anonymous corporate entities. Wall Street, the heart of the country’s financial system, increasingly affected Main Street. Driving the transition was the building of a transcontinental railroad system, which radically altered the scale and scope of American industry. Old industries like iron transformed into modern industries such as the behemoth U.S. Steel. Discovery and invention stimulated new industries, from oil refining to electric light and power. The overbuilding of the railroad in the decades after the Civil War played the key role in transforming the American economy as business came to rely on huge government subsidies, “friends” in Congress, and complicated financial transactions.

Jay Gould in railroads, Andrew Carnegie in steel, and John D. Rockefeller in oil pioneered new strategies to seize markets and consolidate power. Always with an eye to the main chance, these tycoons set the tone in the get-rich-quick era of freewheeling capitalism that came to be called the Gilded Age.