On the 28th June 1914, Archduke Franz Ferdinand of the Austria, heir presumptive to the Austro-Hungarian throne, and his wife Sophie, Duchess of Hohenberg, were shot dead in Sarajevo, by Gavrilo Princip, one of a group of siz assassins (five serbs and one Bosnian Muslim), called The Black Hand.

 The Political objective of the assassination was to break off Austria-Hungary's south-Slav provinces so they could be combined into a Greater Serbia or a Yugoslavia. The assasins motives were consistent with the movement that later became known as Young Bosnia. Serbian military officers stood behind the attack. The assination led directly to the First World War when Austria-Hungary subsequently issued an ultimatum against Serbia, which was partially rejected. Austria-Hungary then declared war, marking the outbreak of the war.

For more information click the wikipedia link below

http://en.wikipedia.org/wiki/Assassination_of_Archduke_Franz_Ferdinand_of_Austria