When Carnegie started in the iron industry, American producers trailed far behind Great Britain in their output. In the 1870s, British industrial output of pig iron was 5.9 million tons per year compared to only 1.8 million tons of American product (which was of such inferior quality that few railroads used it on their lines). Steel production showed an even wider gap. Britain produced 275,000 tons of steel ingot annually compared to America's paltry 37,500 tons per year.
Andrew Carnegie adopted the Bessemer Process for transforming iron into steel in a cheap, high-volume, and efficient manner. He began expanding from iron production to steel and used innovative business management techniques to expand his output and to improve his business. Carnegie eventually vertically integrated his business at the famous Edgar Thompson Works, which used a coordinated delivery system for coke and iron and massive new Bessemer converters to expand his output from 70 tons of steel per week in the 1870s to over 1,000 tons per week in the early 1890s.
Carnegie steel laid the foundation, literally, for modern America. His output included the steel for the Eads Bridge connecting Illinois and St. Louis, MO, across the Mississippi River. The Eads was the world's longest arch bridge at the time of its completion, and contemporary engineers and architects considered its used of steel for the arch to be daring and revolutionary. Opened in 1874, the bridge still stands today and carries vehicle and pedestrian traffic. After the success of the Eads bridge, John Roebling used Carnegie steel in his innovative Brooklyn Bridge. Carnegie's steel output can be found in dozens of skyscrapers and railroads still in use today. By the turn of the century, when Carnegie retired and sold his company to J. P. Morgan, American steel production, much of which came from the Carnegie Steel company, exceeded that of all producers in Great Britain and Germany combined.
J.R.T. Hughes, The Vital Few
Richard Tedlow, Giants of Enterprise
PBS profile of Carnegie for The American Experience
Wikipedia entry on Carnegie