Final answer:
The U.S. Supreme Court deemed certain firms as monopolies because they engaged in anti-competitive practices, dominating the market and harming consumers. Antitrust laws like the Sherman Antitrust Act and the Clayton Antitrust Act were used to break these companies into smaller entities. This led to the dissolution of companies such as Standard Oil and the regulation of unfair business practices by the FTC.
Step-by-step explanation:
The U.S. Supreme Court declared firms like US Steel, Standard Oil, AT&T, and Microsoft as monopolies because they controlled a large share of the market, often through predatory tactics, reducing competition and potentially harming consumers. In response, the U.S. government, leveraging antitrust laws such as the Sherman Antitrust Act of 1890 and the Clayton Antitrust Act of 1914, took action to dissolve these monopolies, leading to the firms being broken up into smaller, independent companies. For instance, the breakup of Standard Oil in 1911 resulted in 34 independent firms, including noteworthy names such as Exxon and Chevron. These acts and the creation of the Federal Trade Commission (FTC) were critical steps in regulating business practices to promote fair competition and protect the consumer.