The four-day Stock Market Crash starting October 24th, 1929, remains the worst Stock Market crash in U.S. History. Another ominous event in our collective memory happened on Monday, October 19th, 1987, when a sudden and largely unexpected stock market crash affected markets around the world. Stock markets fell in Hong Kong (45.5%), Australia (41.8%), Spain (31%), and the United States (22.68%). It was such a bleak day that it has been referenced countless time in popular culture as “Black Monday.”