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Austro-Hungarian Archduke Franz Ferdinand and his wife, Sophie Chotek, are assassinated by Bosnian Serb nationalist Gavrilo Princip. Austria suspects Serbia is responsible.
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Austria-Hungary declares war on Serbia.
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Germany invades Belgium, but is stopped at the First Battle of the Marne. The Schlieffen Plan fails.
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First Battle of Ypres: Attempting to outflank each other, Allied and German troops were unable to win a decisive victory, leading to the onset of trench warfare.
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Britain and France declare war on the Ottoman Empire
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Germany initiates a policy of unrestricted submarine warfare, whereby all merchant ships, including those of neutral countries, would be subject to attack.
