Black Monday occurred on Oct. 19, 1987, when the Dow Jones Industrial Average (DJIA) lost almost 22% in a single day. The event marked the beginning of a global stock market decline, and Black Monday became one of the most notorious days in financial history. By the end of the month, most of the major exchanges had dropped more than 20%—Read more at Investopedia. Kenton, Will. “Black Monday.” 13 September 2019.