Answer:
They established and dominated new steel and oil industries
Step-by-step explanation:
Carnegie and Rockefeller were called the “captains of industry” because they were major industry owners. Both of them were owners of major industries - Steel and oil - which transformed the industry and labor in the US. Both of them dominated the market by creating vertical and horizontal integration, and forcing competitors to close. Carnegie was the responsible to start the railroad industries business in America and Rockefeller started the freight business that also changed America deeply.