ON THIS DAY in 1929, the stock market began its frantic tumble on what became known as Black Thursday. It was followed by Black Friday, Black Monday, Black Tuesday, and Black Wednesday, after which other colors had to be found to indicate rotten days on the market. This precipitous decline in the values of stocks began what is commonly called the Great Depression, a period of global stagnation that ended only with the beginning of the Second World War. From this economic catastrophe American presidents have learned that it is very unwise to allow a single presidential term to pass without a foreign war of some sort.