Austria and Serbia has been involved in several conflict even before the world war 1. They involved in economic conflicts in early 1900s that make the tension between the two countries became quite high, but they still do not have any proper reason to initiate war with one another.
The assassination of Archduke Ferdinand became a perfect trigger for the people who want the war to break out. It became really easy for them to gained support from the citizens to initiate an attack toward Serbia, which lead to the world war 1.
