The largest one-day percentage fall in Dow Jones Industrial Average history occurred on October 19, 1987.
Known as Black Monday, the session saw the Dow Jones Industrial Average fall 508 points, or 22.6 percent. Stock markets in other countries also suffered steep losses, making the event a global market crash rather than an isolated Wall Street decline.
The causes included very high valuations, rising interest rates, trade tensions, and investor concern about the U.S. dollar. Computerized portfolio-insurance strategies and other automated trading practices amplified selling once prices began to fall. Researchers continue to debate the relative importance of these factors.
The 1987 crash differed from 1929 in that the economy did not enter a comparable decade-long depression. Central banks supplied liquidity, and markets eventually recovered. The crash nevertheless prompted reforms to trading systems, including coordinated circuit breakers designed to pause extreme declines.