Final answer:
Rockefeller's success with Standard Oil led to antitrust legislation issues as he consolidated control, leading to an effective monopoly, which directed scrutiny upon his business practices and eventual legal challenges.
Step-by-step explanation:
As John D. Rockefeller's company, Standard Oil, became more successful, he faced the new problem of antitrust legislation. His practice of horizontal integration allowed Standard Oil to merge with or drive out competitors in order to control the market. Once he had a significant share of the market, he would raise oil prices, leveraging his monopoly position. However, his strategies raised concerns about fair competition, which eventually led to government action to break up such monopolies under antitrust laws. This was due to the fact that by the 1890s, Rockefeller’s Standard Oil controlled 90% of the nation's oil refineries, creating a situation where competitive practices were stifled.
Rockefeller's choices, though legal at the onset, eventually contributed to the development and enforcement of antitrust legislation in the United States. The question of legality became significant as the Sherman Antitrust Act of 1890 came into place to prevent such monopolistic actions. His practices have often been the subject of public and legal scrutiny, particularly highlighted by journalists like Ida Tarbell, who exposed the sinister business practices of Standard Oil.