In 1878, Bosnia was occupied by Austria-Hungary; 30 years later, Vienna annexed Bosnia-Herzogovina.
The group that killed Archduke Franz Ferdinand was Mlada Bosna ("Young Bosnia"), a student movement that espoused a heady mix of Nihilism, Pan-Slav nationalism and Russian anarchism. They want to free the people of Bosnia from Austrian-Hungarian occupation.
As per Serbianna.com, Gavrilo Princip (the one who fired the shot that killed the Archduke) could not believe that it caused or resulted in the war. He did not feel responsible for the war and the ensuing “catastrophe”.
He explained that the “old generation” of Serbs (ethnic Serb, not a Serbian national) wanted to achieve change through “a legal way” while the younger generation wanted to achieve it through action, by violence. He, thus, represented the new, radical, revolutionary mindset for achieving social and political change.
Learn more about the First World War centenary, check out the assassination of Franz Ferdinand, as it happened at Telegraph.co.uk.