The 51st Congress, led by Senator John Sherman of Ohio, passed the Sherman Antitrust Act and President Benjamin Harrison signed it in 1890. Its brief text bans anticompetitive agreements and attempts to monopolize, while Senator George Hoar argued that winning business through superior skill was an innocent monopoly. Section 1 covers conspiracies in restraint of trade and Section 2 covers acquiring or keeping monopoly power. Courts judge price fixing as a per se violation and most other conduct under the rule of reason, with a quick look test in between. Defining the market often decides a case, as in the 1966 Grinnell alarm company ruling built on an 87% share of a narrowly drawn market.

The first big targets were workers: in 1893 courts treated a New Orleans general strike as a combination in restraint of trade. The 1937 Apex Hosiery sit-down strike reached the Supreme Court, which sided with the union, and Congress carved out labor through the 1914 Clayton Act and the 1932 Norris-LaGuardia Act. Standard Oil was split into 34 companies in 1911, followed by American Tobacco, AT&T in 1982, Microsoft in 2001 and the current Google litigation. Critics from Alan Greenspan and Ayn Rand to the Chicago School’s Robert Bork and Richard Posner attack the law, while Representative William Mason argued even one-cent oil could not justify crushing competitors.

• Justice William O. Douglas noted that judges read the act loosely for trusts but with strict literalness against unions.
• The 2007 Bell Atlantic v. Twombly decision requires plaintiffs to show a plausible conspiracy, not mere parallel conduct.
• Rockefeller grew richer after the Standard Oil breakup because the pieces were worth more than the whole.
• A 2018 study in Public Choice linked Sherman’s push to his grudge against General Russell Alger over the 1888 convention.
• Economist Thomas DiLorenzo argues the act served as cover while Republicans passed the protectionist McKinley Tariff.