What was the first U.S. stock-market crash widely attributed to computerized program trading?

Black Monday 1987 was the first major U.S. stock-market crash widely associated with computerized program trading.

On October 19, 1987, the Dow Jones Industrial Average plunged 22.6%, its largest one-day percentage decline. Program trading systems automatically executed large orders based on market movements, and portfolio insurance strategies could generate additional selling as prices dropped.

Computerized trading was not the only cause. Investors were also worried about interest rates, exchange rates, trade deficits, and high valuations. Researchers and regulators have therefore treated the technology as an amplifier of pressure rather than a complete explanation for the crash.

The episode led to important changes in market structure. Exchanges introduced circuit breakers and other safeguards intended to pause trading during extreme movements. The 2010 Flash Crash was a later, distinct event involving automated trading.