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Bosnian Serb, Gavrilo Princip, killed Archduke Francis Ferdinand of Austria and his wife Sofia in Sarajevo on June 28, 1914, setting off a chain of events that would culminate in a world war by August.
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On July 28, 1914, after a report of an unverified incident involving Hapsburg and Serbian troops, the government of Austria-Hungary declared war on Serbia. World War I was fought on three continents and across the world's major oceans.
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Great Britain declared war on Germany at 11:00 p.m. for violating Belgian neutrality. The United States declared neutrality at the outbreak of World War I. With Great Britain formally at war, the Dominions of Australia, Canada, and New Zealand entered World War I.
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On May 7, 1915, the German U-20 (submarine) sank the British ocean liner Lusitania. Approximately 1,200 civilians died; more than 100 were U.S. citizens. The Lusitania carried both passengers and ammunition that had been manufactured in the United States.
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Third Battle of Artois. The Allied offensive to recapture French territory from the Germans on the Western Front ended in failure. France lost 48,320 casualties while Great Britain lost 61,713.
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January 19, 1917 - The British intercept a telegram sent by Alfred Zimmermann in the German Foreign Office to the German embassies in Washington, D.C., and Mexico City.
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U.S. Enters World War I. On April 6, 1917, the United States formally declared war against Germany and entered the conflict in Europe. Fighting since the summer of 1914, Britain, France, and Russia welcomed news that American troops and supplies would be directed toward the Allied war effort.
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Shock troops with the Austro-Hungarian Army pushed 11 Italian divisions off the Mount Ortigara summit, regaining their important defensive position in Asiago, Italy. Italy suffered 23,000 casualties while Austria-Hungary sustained only 9,000 casualties
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The Allied powers signed a ceasefire agreement with Germany at Compiégne, France, at 11:00 a.m. on November 11, 1918, bringing the war now known as World War I to a close. Between the world wars, November 11 was commemorated as Armistice Day in the United States, Great Britain, and France.
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The Treaty of Versailles was the primary treaty produced by the Paris Peace Conference at the end of World War I. It was signed on June 28, 1919, by the Allied and associated powers and by Germany in the Hall of Mirrors in the Palace of Versailles and went into effect on January 10, 1920.
