The full version of my answer:
The Sherman Antitrust Act of 1890 is a United States antitrust law that regulates competition among enterprises that was passed by Congress under the presidency of Benjamin Harrison. It is named for Senator John
Sherman, its principal author. The Sherman antitrust act outlaws "every contract, combination, or conspiracy in restraint of trade," and any "monopolization, attempted monopolization, or conspiracy or combination to monopolize." Long ago, the Supreme Court decided that the Sherman
Act does not prohibit every restraint of trade, only those that are. For more than a decade after its passage, the Sherman Antitrust Act was invoked only rarely against industrial monopolies, and then not successfully. Ironically, its only effective use for a number of years was against labor unions, which were held by the courts to be illegal combinations.
A more simple paragraph of the answer:
The Sherman Antitrust Act of 1890 is a United States antitrust law that regulates competition among enterprises that was passed by Congress, Long ago, the Supreme Court decided that the Sherman Act does not prohibit every restraint of trade, only those that are. For more than a decade after its passage, the Sherman Antitrust Act was invoked only rarely against industrial monopolies, and then not successfully.