Final answer:
The most important antitrust law in American history is the Sherman Antitrust Act of 1890, designed to limit the power of monopolies and trusts influencing free trade and economic competition.
Step-by-step explanation:
The most important antitrust law in American history was the Sherman Antitrust Act of 1890. This groundbreaking federal legislation was passed to curb concentrations of power that interfere with trade and reduce economic competition. It authorized the federal government to dissolve corporations that were deemed to be acting in restraint of free trade, such as by forming monopolies or engaging in other anti-competitive practices. One of the landmark demonstrations of the Act's authority came in 1911, when the U.S. Supreme Court sanctioned the breakup of Standard Oil, effectively ending its control of about 90% of America's oil refining business. Subsequent antitrust laws and regulatory bodies, including the Clayton Antitrust Act and the Federal Trade Commission, have built on the foundation established by the Sherman Antitrust Act to ensure fair competition in the market.