type: timeline_event Andrew Carnegie opened the Edgar Thomson Steel Works in Braddock, Pennsylvania, in 1875, effectively introducing the Bessemer steelmaking process to the United States at industrial scale and launching his steel empire. Construction had begun in 1872, with the mill beginning rail production in 1874. The Bessemer process enabled mass production of steel, allowing steel to replace iron as the metal of choice in construction, railroads, and manufacturing—transforming American industry. Carnegie named the facility after J. Edgar Thomson, president of the Pennsylvania Railroad, both to honor a business connection and to signal that Carnegie Steel would be a reliable supplier to the railroad industry, which consumed vast quantities of steel rails. This mill became the foundation for Carnegie's vertical integration strategy: rather than simply operating steel mills, Carnegie systematically acquired iron ore mines, coal fields, limestone quarries, coke ovens, ships, railroads, and every other component of the steel supply chain. This vertical integration allowed Carnegie to control costs at every stage of production, undercutting competitors who had to purchase raw materials at market prices. The Edgar Thomson Works represented the beginning of systematic industrial consolidation that would culminate in Carnegie's 1892 formation of Carnegie Steel Company and his eventual 1901 sale to J.P. Morgan for $480 million, creating U.S. Steel, the world's first billion-dollar corporation. Carnegie's model—vertical integration, cost control, technological innovation, and aggressive elimination of competitors—became the template for industrial dominance that parallels modern tech platforms' control of entire technology stacks from chips to cloud services to consumer applications.