October 19, 1987, the day of the 1987 global stock-market crash, was known as Black Monday.
The Dow Jones Industrial Average fell 508 points, or 22.6 percent, in one session. That percentage decline remains the largest single-day percentage loss in the index's history. Stock markets in other countries also fell sharply, making the event a genuinely international crash rather than a problem confined to New York.
Several explanations have been proposed, including overvalued shares, investor anxiety, portfolio insurance, and computerized trading strategies. No single cause accounts for every market's movements. Regulators later introduced circuit breakers and other safeguards designed to pause trading during extreme price swings. Black Monday is distinct from the 1929 crash dates, which also use “Black” weekday nicknames.