Who led the steel industry in the United States by employing vertical integration?

Andrew Carnegie is recognized for leading the steel industry in the United States through the strategy of vertical integration. This approach involves controlling every aspect of the production process from raw materials to transportation to manufacturing and distribution. Carnegie's acquisition of iron mines, railroads, and steel mills allowed him to reduce costs and enhance efficiency, making his company one of the leading steel producers of its time.

His ability to integrate these different stages of production not only positioned him as a titan of industry but also significantly lowered prices for consumers while increasing production capabilities. This method also fostered more competitive marketplaces as it demonstrated the benefits of owning and managing multiple facets of a supply chain. The figures mentioned in the other options, while influential in their respective industries—such as Vanderbilt in railroads and Rockefeller in oil—did not employ vertical integration in the steel sector in the same impactful way that Carnegie did.