World War I (United States)

On June 28, 1914, Archduke Franz Ferdinand of Austria-Hungary was assassinated by a Serbian nationalist, Gavrilo Princip. Austria-Hungary then issued an ultimatum of demands, to which Serbia failed to reply. Within a month, two coalitions had formed in Europe, the Allied Powers (France, Russia, and Great Britain) and the Central Powers (Germany, Austria-Hungary, and Italy). World War I had begun. The US officially remained neutral in the war until April 1, 1917 when German U-boats torpedoed the S.S. Aztec, killing twenty-eight Americans. The war continued for another year and a half, formally ending on November 11, 1918, when Germany signed the Armistice. World War I is considered one of the deadliest conflicts in history, with an estimated nine million combatant and seven million civilian deaths resulting directly from the war.