There is no single cause for World War One. The catalyst for the war was the assassination of Archduke Franz Ferdinand of Austria by a Serbian nationalist. At that point the Austro-Hungarian Empire controlled a great deal of the Slavic territories (today Croatia, Slovenia and Bosnia-Herzegovina) and the assassin was committed to the unification of the region and Slavic peoples. He aimed at provoking a crisis that would weaken the Empire. Apart from this, imperialism and nationalism throughout Europe exacerbated tensions. Countries began to create alliances that pitted the different sides against each other creating greater divisions. When diplomacy failed World War I broke out.
