Black Monday was the October 1987 event that caused stock markets worldwide to suffer their largest one-day falls in decades. The date was October 19, 1987, when major markets plunged in a synchronized wave of selling.
The crisis was not limited to the United States. Hong Kong’s market fell first, followed by severe declines in Europe, Australia, Canada, and the United States. The Dow Jones Industrial Average dropped 22.6%, while the S&P 500 fell by more than 20% in a single session.
Several pressures contributed. Share prices had risen strongly, interest rates were elevated, and investors worried about trade and currency tensions. Program trading and portfolio-insurance strategies could automatically sell into a falling market, intensifying the downward movement. The precise balance among these causes remains debated.
Black Monday is sometimes confused with the 1929 crash days, which also use “Black” labels. The 1987 event is distinctive because it was exceptionally international and because its percentage decline was concentrated in one trading day rather than spread across a longer collapse.