The New York Stock Exchange closed due to the outbreak of World War I. (Trading didn't resume until December.)
On July 31, 1914, the New York Stock Exchange closed its doors for the longest period in exchange history. It stayed closed until Nov. 28, 1914, when bonds began trading again. Stock trading re-opened Dec. 15, 1914, but shares were not allowed to trade below closing prices of July 30, 1914. By April 1, 1915, all trading was re-established without price limits. Most would dismiss the closing as a natural response to the beginning of World War I. But no war before or after (including the Civil War), or even the devastating attack on the World Trade Center less than one-half mile from the NYSE in 2001, has shuttered the exchange for more than 10 days in its 222-year history.