How did john d Rockefeller and Andrew carnage make their money?

John D. Rockefeller made his fortune primarily through the oil industry by founding Standard Oil, which dominated the U.S. petroleum market in the late 19th century through strategic practices such as horizontal integration and aggressive pricing. Andrew Carnegie amassed his wealth in the steel industry, establishing Carnegie Steel Company, which became the largest and most profitable steel company in the world by utilizing innovative production techniques and vertical integration. Both men were pivotal in shaping American industry during the Gilded Age and became symbols of wealth and philanthropy.