Black Monday was the 1987 crash in which markets fell sharply around the world on the same day.
On October 19, 1987, major stock markets experienced extraordinary declines. The Dow Jones Industrial Average fell 22.6 percent in one session, while markets in Hong Kong, Australia, the United Kingdom, and elsewhere also suffered severe losses. The synchronized movement reflected increasingly connected global finance.
Researchers have identified several contributing factors, including valuation concerns, portfolio-insurance strategies, computerized trading, and international economic tensions. The crash did not produce a depression comparable to the 1930s, and the U.S. economy continued to expand. The name can cause confusion because “Black Monday” is also used for other market declines, but the 1987 date is the best-known reference.