Black Monday describes the October 19, 1987 crash when stock markets around the world plunged sharply in one day. In the United States, the Dow Jones Industrial Average fell 22.6%, its largest one-day percentage decline.
The name refers specifically to the date in the United States, although the global sell-off unfolded across several trading sessions because markets opened at different times. Hong Kong fell first, followed by European markets and then New York. Australia and Canada also experienced major losses.
Researchers have identified several contributing factors rather than one universally accepted cause. Valuations were high, interest-rate concerns were present, and computerized portfolio-insurance strategies encouraged further selling as prices declined. Afterward, regulators introduced coordinated trading halts and circuit breakers designed to give investors time to assess extreme moves.