After the mid-nineteenth century, the development of machine-powered mass-manufacturing techniques powered the American economy. It had begun in the textile industry, whose mills had provided jobs for large numbers of the Irish immigrants who were then beginning to enter the United States. However, mass manufacturing extended well beyond the textile industry and became, in a sense, self-generating. As increasingly large factories required ever greater quantities of materials to operate, their needs spurred the development of other industries. For example, the railroads required steel in huge quantities for their thousands of miles of rails and for the trains themselves. The steamships and ferries that were beginning to move passengers and cargoes at previously unimagined speeds needed giant foundries to manufacture the plates that formed them and the engines that powered them.
The immense demands for the iron alloys from which to fashion the new machines created a steel industry whose size was empowered by the Bessemer process that was invented in 1855 but only widely adopted after the U.S. Civil War (1861- 1865). The Bessemer process made possible the vast steel mills of Pittsburgh and other cities, and the steel industry in turn contributed to the great expansion of the coal-mining industry, which was also beginning to supply great amounts of fuel to railroads and steamships. Through the late nineteenth century, coal mining employed huge numbers of unskilled immigrant laborers.
One of the ultimate achievements of the Industrial Revolution was the creation of assembly-line production that Henry Ford introduced to automobile manufacturing during the early twentieth century. To the system of interchangeable parts, assembly lines added the advantage of simplifying the tasks performed by individual workers to make large-scale manufacturing more profitable. Simplification of workers’ tasks opened many jobs to unskilled immigrant workers.