The single-day 1987 stock-market collapse that struck markets worldwide was called Black Monday.
Black Monday occurred on October 19, 1987. The Dow Jones Industrial Average fell 508 points, or 22.6 percent, in one session, its largest one-day percentage decline. Markets in Hong Kong, London, and other financial centers also suffered severe falls, making the event international rather than purely American.
Explanations for the crash include overvalued shares, a growing trade deficit, currency tensions, and computerized portfolio-insurance strategies that encouraged selling as prices dropped. Regulators later introduced circuit breakers and other trading safeguards. Black Monday is often confused with the 1929 crash because both became associated with a weekday color label, but they were separate events nearly six decades apart.