What business contributed most to Andrew Carnegies ability to form a monopoly?

Andrew Carnegie's ability to form a monopoly was primarily driven by his investments in the steel industry, specifically through the establishment of Carnegie Steel Company. By implementing innovative production techniques, such as the Bessemer process, and focusing on vertical integration, Carnegie was able to control every aspect of steel production, from raw materials to transportation. This dominance in the steel market allowed him to eliminate competition and establish a near-monopoly in the industry by the late 19th century.