October was the month of the 1929 Wall Street crash's famous two-session collapse.
The first major panic session came on October 24, 1929, later called Black Thursday. After a brief weekend recovery attempt, selling intensified on October 28 and October 29. October 29 became known as Black Tuesday, when about 16 million shares changed hands and prices fell sharply.
The crash did not end on October 29. The Dow Jones Industrial Average continued declining, eventually reaching its bear-market low in July 1932. The market collapse was one major part of a wider economic breakdown involving bank failures, unemployment, deflation, and falling production.
September is sometimes chosen because the market had reached a peak earlier in that month, while November contains further damaging sessions. The best-known crash dates, however, all fall in October. The later Great Depression affected many countries and cannot be explained solely by the mechanics of stock trading.