Why did Austria announce the war against Serbia?

1)       Austria had been determined to capture Balkan region.
2)       For this reason, there was a conflict between Austria and Serbia over Bosnia and Herzegovina.
3)       Austria annexed Bosnia and Herzegovina which created great unrest and grievance over Balkan region.
4)       Royal representative of Austria, Prince Archduke Ferdinand was assassinated at Sarajevo, Bosnian capital by an extremist Serbian citizen.
5)       In retaliation, Austria imposed unacceptable demands on Serbia which were to be fulfilled within 48 hours.
6)       Russia supported Serbia and with her support, emboldened Serbia refused to accept the demand of Austria.
As a result Austria declared war on Serbia on 28th July 1914