The 1987 market event that caused stock exchanges worldwide to plunge together after the U.S. sell-off was Black Monday.
Black Monday refers to October 19, 1987, when stock markets around the world suffered an extraordinary synchronized decline. The Dow Jones Industrial Average fell 22.6% in one session, while markets in several other countries recorded even larger percentage losses.
Several factors were blamed or investigated, including overvalued shares, rising interest rates, trade tensions, portfolio insurance, and computer-driven selling. No single explanation fully accounts for the global speed and scale of the fall.
Black Monday is distinct from the Black Monday of 1929-era Wall Street history, a term sometimes used for October 28, 1929. The 1987 crash did not produce a depression comparable to the 1930s, and many markets recovered substantially in the following years.