The 1987 global stock-market crash was called Black Monday in the United States, where the Dow fell 22.6% in one session.
Black Monday refers specifically to October 19, 1987. The Dow Jones Industrial Average lost 508 points, a fall of 22.6%, while the S&P 500 and other major indexes also suffered dramatic declines. The crash was international: Hong Kong and European markets had already dropped, and markets in Australia and New Zealand were affected as well.
Several pressures contributed. Share valuations were high, interest rates were rising, and investors were worried about trade and currency tensions. Portfolio insurance programs and other automated selling strategies could turn falling prices into additional sell orders, accelerating the decline.
The name can cause confusion because “Black Monday” has been used for other market collapses, including October 28, 1929. In the context of the 1987 crash, however, it identifies October 19. Regulatory responses included market-wide circuit breakers and improvements to coordination among exchanges and financial authorities.