The Dow Jones Industrial Average lost 22.6% on October 19, 1987, the largest one-day percentage decline in its history.
That Monday became known as Black Monday. Stock markets fell across the world, with especially severe declines in Hong Kong, Australia, the United Kingdom, Canada, and the United States. The Dow’s fall exceeded the percentage loss recorded on the most famous single day of the 1929 crash.
Several factors were discussed afterward, including rising valuations, fears about interest rates and trade, and computerized portfolio-insurance strategies that could intensify selling. No single cause fully explains the global event.
The 1987 crash did not lead to a depression comparable to the 1930s. Central banks supplied liquidity, and the U.S. Federal Reserve publicly signaled its readiness to support the financial system. The Dow eventually recovered, but the episode changed market regulation and trading safeguards.