The 19 October 1987 stock-market crash in Hong Kong, Britain, and the United States was called Black Monday.
The date became associated with a synchronized worldwide collapse. Hong Kong’s market fell first because of time-zone differences, followed by major European exchanges and Wall Street. The Dow Jones Industrial Average lost 22.6 percent in the United States.
The crash showed how quickly international financial markets had become connected. Computerized trading, derivatives, portfolio insurance, and cross-border investment could transmit selling pressure from one exchange to another.
Black Monday is not the same as Black Monday in 2020, a term also used for several market sell-offs. In stock-market history, the unqualified phrase most often means the global crash of 19 October 1987.