October 19, 1987, saw the Dow Jones Industrial Average lose 22.6%, the largest one-day percentage fall in its history.
The worldwide sell-off became known as Black Monday. The Dow fell 508 points, while major markets in Europe, Asia, Australia, and Canada also suffered sharp declines. The percentage loss remains larger than any single-day fall during the 1929 crash or the 2008 financial crisis.
Several forces contributed. Valuations were high, interest rates had risen, and investors were increasingly using computerized portfolio-insurance strategies that automatically sold futures as prices fell. Those sales intensified the downward spiral, although historians do not identify one single cause.
The crash did not produce a 1930s-style depression. Central banks supplied liquidity, exchanges introduced circuit breakers, and markets eventually recovered. A common mix-up is confusing Black Monday with Black Tuesday in 1929; the two events occurred 58 years apart.