Andrew Carnegie was largely responsible for the great advances in steel production. Carnegie, who came to America from Scotland as a child of 12, progressed from bobbin boy in a cotton factory to a job in a telegraph office, then to one on the Pennsylvania Railroad. Before he was 30 years old he had made shrewd and farsighted investments, which by 1865 were concentrated in iron. Within a few years, he had organized or had stock in companies making iron bridges, rails, and locomotives. Ten years later, he built the nation's largest steel mill on the Monongahela River in Pennsylvania.  He acquired control not only of new mills, but also of coke and coal properties, iron ore from Lake Superior, a fleet of steamers on the Great Lakes, a port town on Lake Erie, and a connecting railroad. His business, allied with a dozen others, commanded favorable terms from railroads and shipping lines. Nothing comparable in industrial growth had ever been seen in America before.

Though Carnegie long dominated the industry, he never achieved a complete monopoly over the natural resources, transportation, and industrial plants involved in the making of steel. In the 1890s, new companies challenged his preeminence.  He would be persuaded to merge his holdings into a new corporation that would embrace most of the important iron and steel properties in the nation.