Black Monday prompted the creation of automatic trading circuit breakers in the United States.
On October 19, 1987, the Dow Jones Industrial Average plunged 22.6%, its largest one-day percentage loss. The speed and breadth of the decline raised concerns that computerized trading, portfolio insurance, and crowded positions could amplify selling before human investors had time to respond.
After the crash, U.S. regulators and exchanges developed mechanisms that temporarily halt trading when prices move beyond specified thresholds. These pauses are commonly called circuit breakers. Their purpose is to give market participants time to absorb information, restore orderly communication, and reduce panic-driven feedback loops.
Circuit breakers do not prevent losses or guarantee that prices will stabilize. They are a market-structure response designed to slow extreme moves. The rules have been revised over time, including after later episodes such as the 2010 Flash Crash. Black Monday therefore influenced not only investor behavior but also the architecture of modern exchanges.