World War I

World War I. . , Triggered by the assassination of Archduke Franz Ferdinand, the heir to the throne of the Austro-Hungarian Empire, World War I began in August 1914 when Germany invaded Belgium and France. On the Eastern front, Russia agreed to stop fighting late in 1917 following the Russian Revolution. The Western front was stalemated in trench warfare for three-and-a-half years before the United States intervened in 1917 on the side of the Allies., Several events led to U.S. intervention: the sinking of the Lusitania, a British passenger liner; unrestricted German submarine warfare; and the Zimmerman Note, which revealed a German plot to provoke Mexico to war against the United States., World War I killed more people--9 million combatants and 5 million civilians--and cost more money--$186 billion in direct costs and another $151 billion in indirect costs--than any previous war in history. Politically, it resulted in the downfall of four empires and contributed to the Bolshevik rise to power in Russia in 1917 and the triumph of Fascism in Italy in 1922. The war allowed the United States to become the world's leading creditor and industrial power. Its consequences included the mass murder of Armenians in Turkey and an influenza epidemic that killed over 25 million people worldwide.