 In 1894, the U.S. Congress declared the first Monday of September to be Labor Day, a holiday to honor the American worker. On this day in 1914, Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, and his consort Sophie were assassinated by Gavrilo Princip in Sarajevo, Bosnia, precipitating the outbreak of World War I. In 1919, the Treaty of Versailles was signed at the Palace of Versailles in France, signifying the end of World War I.