That is where the target (Archduke Franz Ferdinand) was at.
It was a failed attempt aimed at Archduke Franz Ferdinand using a grenade.
On 28 June 1914.
Because of the numerous alliances which brought German support to Austria and Russian support to Serbia, Bosnia and Herzogovinia. The French and the UK were sucked in to provide support to Russia....
Because the assassination did lead to the world war 1.