The Road to Black Monday the Worst Day in Wall Street History. Monday, October 19, 1987, was by far the worst day in Wall Street history. The market fell 22.6 percent - almost twice as bad as the worst day of 1929 - equal to a loss of more than 4,000 points today. But Black Monday was more than just a one-day market crash it was seven years in the making and threatened the entire U.S. financial system. Drawing on superlative archival research and dozens of original interviews, Diana B. Henriques weaves a tale of ignored warnings, market delusions, and destructive decisions, a drama that stretches from New York and Washington to Chicago