Black Monday occurred on October 19, 1987, when the Dow Jones Industrial Average suffered its largest one-day percentage decline.
The Dow fell 508 points, or 22.6%, in a single trading session. The decline was unusually severe because it happened across markets worldwide, including Hong Kong, London, and Australia. The crash followed a sharp rise in share prices earlier in the decade.
Several factors contributed, including concerns about trade deficits, interest rates, computerized trading, and portfolio-insurance strategies. The exact balance among these causes remains debated. Unlike the 1929 crash, Black Monday did not lead to a decade-long economic depression.
The U.S. Securities and Exchange Commission and the Federal Reserve later introduced safeguards, including market-wide trading halts known as circuit breakers. These mechanisms were designed to give investors time to assess rapidly falling prices.