Answer:
Serbian nationalist Gavrilo Princip
Step-by-step explanation:
Because he killed Archduke Franz Ferdinand heir to the Austro-Hungarian Empire. Because of this, Austria-Hungary declares war on Serbia, effectively beginning the First World War.
Gavrilo Princip, a member of the black hand society, assassinated Archduke Franz Ferdinand and his wife, triggering the military alliances that declared on each other consecutively.
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