The 22.6% one-day fall in U.S. share prices on October 19, 1987, was called Black Monday.
The Dow Jones Industrial Average dropped 508 points, or 22.6 percent, in its largest one-day percentage decline. Selling spread rapidly across international markets, including Hong Kong, Australia, the United Kingdom, and Canada. The collapse was unusually sudden: unlike the long deterioration associated with 1929, much of the damage occurred within a single trading day.
Several explanations have been studied. Computer-assisted trading, portfolio insurance, overvaluation, rising interest rates, and international economic tensions all contributed to the market’s vulnerability. No single cause fully explains the event, and investigators continue to distinguish between factors that increased selling and those that amplified it.
The crash did not lead to a depression comparable to the 1930s. The Federal Reserve, led by Alan Greenspan, reassured markets about its readiness to provide liquidity. New trading safeguards, including circuit breakers, were later introduced to slow extreme declines.