Black Monday was the 1987 crash in which the Dow Jones Industrial Average fell 22.6% in one day.
The event took place on 19 October 1987. It was not confined to the United States: stock markets around the world fell, making it an early demonstration of how closely connected modern financial centers had become. The Dow’s 508-point drop was the largest one-day percentage decline in its history.
Several pressures were present, including high valuations, rising interest rates, a strong U.S. dollar, and worries about trade. Automated trading and portfolio-insurance programs also accelerated selling. Because prices could move faster than investors could reassess the underlying companies, the fall became unusually rapid.
The crash did not produce a Great Depression-style collapse in the real economy. The Federal Reserve supplied liquidity and publicly signaled its willingness to support the financial system. Market institutions later introduced circuit breakers to pause trading during extreme declines, a safeguard still used in modified form today.