The New York Stock Exchange (NYSE) at the outbreak of WWI.

July 30, 1914: the New York Stock Exchange (NYSE) closed due to the outbreak of WWI. It remained closed till December 12 of 1914, the longest period in exchange history. During that time stocks were quoted by brokers and traded off the exchange.

 Austria-Hungary declared war on Serbia on July 28, 1914, causing Germany and Russia to mobilize their armies on July 30. When Russia offered to negotiate rather than demobilize their army, Germany declared war on Russia on August 1. Germany declared war on France on August 3, and when Germany attacked Belgium on August 4, England declared war on Germany.