Black Monday refers to October 19, 1987, when stock markets around the world crashed and the Dow Jones Industrial Average fell about 22.6 percent in one trading session.
What happened
The crash spread across markets rather than staying local. Selling pressure in one market fed into others, and attempts to hedge falling equity prices intensified the decline. Portfolio-insurance strategies, thin liquidity, and fear-driven trading all reinforced the downward move.
This mattered because market structure and investor behavior interacted. Prices did not simply fall because fundamentals changed in one instant. They fell because many participants tried to adjust at the same time in an environment where markets could not absorb the order flow smoothly.
Why economists study it
Black Monday is a major case in financial economics because it highlights:
- the role of liquidity in price formation,
- feedback trading and market microstructure,
- contagion across linked markets,
- the difference between a market crash and a full macroeconomic depression.
The crash did not trigger another Great Depression, but it did change policy and exchange design. Later use of circuit breakers and other safeguards was shaped by lessons from 1987.
Economic significance
Black Monday reminds economists that asset prices can move violently even when standard macroeconomic data do not justify such a dramatic one-day adjustment. It is therefore a useful example when discussing volatility, expectations, and systemic risk.