United States v. Microsoft (1998-2001)
The DOJ sued Microsoft for monopolizing the PC operating system market by tying Internet Explorer to Windows. Judge Thomas Penfield Jackson ordered Microsoft split into two companies. The D.C. Circuit Court of Appeals overturned the breakup, and the case settled in 2001.
Microsoft avoided breakup; the settlement imposed behavioral remedies requiring API disclosure and non-discrimination against rivals.
The settlement is widely credited with letting competitors like Mozilla and Google's Chrome emerge, but critics say it arrived too late to matter.
The Microsoft case is the closest precedent: a federal court finding a tech monopoly, the DOJ seeking breakup, and appellate rejection ending in behavioral remedies instead—exactly the pattern Google's ad tech case is following.
