Advanced Placement US History (AP US History) Practice Exam

John D. Rockefeller is most closely associated with the oil industry, particularly through his company, Standard Oil. Founded in 1870, Standard Oil grew to dominate the oil refining sector, controlling around 90% of U.S. refineries and pipelines at its peak. Rockefeller's innovative business strategies, including horizontal integration, allowed him to eliminate competition and create a monopoly that influenced prices and production standards throughout the industry.

His involvement in oil was significant during the industrialization of America, as oil became a crucial energy source, powering machinery, locomotives, and eventually automobiles. This transformation led to substantial economic growth and changed the landscape of the American economy in the late 19th and early 20th centuries. In contrast, the other industries mentioned—steel, transportation, and agriculture—are not primarily linked to Rockefeller's legacy. While transportation and steel were critical to industrial growth, figures like Andrew Carnegie are more closely associated with steel, and various railroad tycoons are linked with transportation. Agriculture also does not reflect Rockefeller's contributions, as his focus remained on the oil sector.