Black Monday (1987)

Black Monday remains one of the most studied single-day market events in financial history. On October 19, 1987, the Dow Jones Industrial Average plunged 508 points, equivalent to a 22.6% loss in a single session. To put that in context, the 2008 financial crisis — widely remembered as catastrophic — never produced a single-day loss of more than 8% on the Dow. The speed and severity of the 1987 crash shocked even seasoned market participants.

Several structural factors contributed to the crash. Portfolio insurance, a hedging strategy popularized in the early 1980s, instructed institutional managers to automatically sell stock index futures as portfolio values declined, locking in losses and protecting a floor. When markets began falling, the automated selling triggered further declines, which triggered more selling — a feedback loop that overwhelmed normal market-making capacity. Computer-driven program trading amplified each wave of selling.

Macroeconomic concerns had already unsettled markets in the days leading up to October 19. The US trade deficit had widened significantly, and the Treasury Secretary had publicly suggested the dollar should weaken further — raising fears of inflation and higher interest rates. Global markets had also been weakening, with London and Hong Kong recording sharp declines in the days prior.

The crash was remarkable for what it did not produce: a recession. The Federal Reserve, led by Alan Greenspan who had taken office just two months earlier, swiftly announced its readiness to supply liquidity to the financial system. This response prevented the stock market crash from freezing credit markets and spilling into the broader economy, a lesson that informed central bank responses in later crises.

In the aftermath, US regulators introduced circuit breakers — automatic trading halts triggered by large percentage declines — to slow panic selling and allow markets to regain equilibrium. These circuit breaker rules were subsequently revised and strengthened following the 2010 Flash Crash. Black Monday also prompted a fundamental rethinking of risk management models, many of which had assigned near-zero probability to a one-day loss of that magnitude.