How did Rockefeller establish a monopoly?

John D. Rockefeller established a monopoly in the oil industry primarily through aggressive business practices, including horizontal integration. He founded the Standard Oil Company in 1870 and systematically acquired competing oil refineries, thus controlling a significant share of the market. Additionally, he negotiated favorable rates with railroads for oil transportation, undercutting competitors' prices and driving them out of business. This combination of strategic acquisitions and competitive pricing allowed Rockefeller to dominate the oil industry and effectively eliminate competition.