Antitrust Action

Antitrust action describes the set of moves available to government to constrain concentrated market power. The major categories:

• Merger review and blocks: agencies (DOJ Antitrust Division, FTC) can sue to prevent or unwind mergers above HHI thresholds, or where market-share concentration is judged anticompetitive.
• Monopolization suits: lawsuits alleging an existing dominant firm is using its position to exclude rivals (the modern Google search trial, the Microsoft case in the late 1990s).
• Structural remedies: court-ordered breakups (AT&T 1984, Standard Oil 1911), or behavioral injunctions short of breakup.
• Rule-making and merger guidelines: agencies can update the framework under which mergers are reviewed, raising or lowering the bar.

The 2020s have seen the largest revival of antitrust enforcement since the Reagan era — Khan-doctrine FTC cases, DOJ challenges to large mergers, state-AG coalitions filing in parallel. Whether enforcement actions translate to durable structural change depends on appellate outcomes and whether successor administrations continue or roll back the cases.