The largest one-day percentage fall in the 1987 global stock-market crash was nicknamed Black Monday.
On October 19, 1987, the Dow Jones Industrial Average fell 22.6 percent, its largest one-day percentage decline. Markets in other countries also dropped sharply, making the event an international crash rather than an isolated U.S. sell-off.
Several factors were associated with the collapse, including high valuations, investor concerns about economic conditions, trade tensions, and computerized portfolio-insurance strategies. Those automated selling programs could intensify downward momentum when prices fell.
Black Monday is not the same event as the 1929 day also called Black Tuesday, or the 2020 market shock during the COVID-19 pandemic. The 1987 crash was followed by policy responses and a relatively quick market recovery compared with the prolonged decline after 1929.