The 1987 stock-market crash in which the FTSE 100 fell more than 10% on October 20 was known as Black Monday. The name usually refers to the international crash that began in Hong Kong on October 19 and reached markets around the world over the following days.
The U.K. market’s October 20 decline was part of a global sequence rather than an isolated London event. Currency tensions, concerns about interest rates and trade deficits, and automated portfolio-insurance strategies all contributed to the turbulent conditions.
The United States had its most dramatic session on October 19, when the Dow Jones Industrial Average lost 22.6% in one day. That was the largest percentage fall in the Dow’s history, but other national markets also suffered extraordinary losses.
The term can cause confusion because “Black Monday” has been used for other market declines, including the U.S. crash of October 28, 1929. In the context of the worldwide 1987 event, it refers to October 19 and the international trading turmoil surrounding it.