The stock-market crash that began on October 19, 1987, after Hong Kong’s market had plunged was Black Monday. The name is most strongly associated with the worldwide market collapse of that date.
Hong Kong’s Hang Seng Index fell sharply on October 19, and selling pressure moved through other Asian and European markets before the New York Stock Exchange opened. By the close in New York, the Dow Jones Industrial Average had lost 22.6%, its largest one-day percentage decline.
The crash demonstrated that market shocks could travel rapidly across time zones. Modern communications, international investment, derivatives, and automated trading connected exchanges more closely than in earlier decades. The episode prompted regulators to examine trading systems and eventually contributed to the development of circuit breakers that can pause trading during extreme moves.
Black Monday is sometimes confused with Black Monday in 1929, which occurred on October 28 of that year. The shared label refers to different crashes, so the year is essential when identifying the event.