The Bessemer process was one in which steel could be made more efficiently and with less impurities than previously possible. Carneige, a rich business owner at this time, took advantage of this process in order to produce a significant amount of steel.
This process resulted in the ability to make steel faster and more efficiently. This drove down the cost of developing this steel and resulted in more companies being able to afford it.
Carneige's success with this process helped him to become a monopoly, as he was the first to use this process in the United States. Nobody could compete with his prices and the amount of steel he could produce. This would result in Carneige developing an enormous personal fortune.