Final answer:
John D. Rockefeller's Standard Oil Company achieved financial success through controlling the oil industry, using horizontal integration and forming trusts to consolidate his empire.
Step-by-step explanation:
John D. Rockefeller and the Standard Oil Company achieved financial success by controlling the oil industry. Starting with about three percent of the nation's oil in 1870, Rockefeller expanded his control through strategic practices like horizontal integration, where he either merged with other oil firms or drove them out of the market. These tactics allowed him to control prices by lowering them to eliminate competition and later raising them when he dominated the market. By employing trusts and holding companies, Rockefeller was able to legally consolidate his holdings and circumvent monopoly laws of the time, eventually controlling 90 percent of the nation's oil refineries. His business methods would set a precedent for other industry titans who followed by forming similar trusts.