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Austria-Hungary asked Serbia to help with the investigation into the assassination, but Serbia refused, so Austria-Hungary declared war on Serbia
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Archduke of Franz Ferdinand was assassinated by members of the Black Hand.
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Germany began sinking Allied ships with U-boats
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Germany sank the British passenger ship holding American called the Lusitania
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The United States were starting to prepare for the possibility of war
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Wilson asks Congress for a declaration of war
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Congress declares war on Germany
