They blame it on Serbia. It was their terrorist organization called the Black Hand that killed him (and his wife).
Serbia
Austria-Hungary blamed Serbia for the assassination. The assassination happened in Bosnia, which was ruled by Austria-Hungary at the time; Bosnian separatists murdered the Archduke with some assistance from Serbian intelligence officials. The Austrian government, of course, found out about this and was not too happy.
Austria-Hungary
Austria-Hungary.
It was the Archduke Franz (or Francis) Ferdinand of Austria, heir to the throne of Austria-Hungary, assassinated in Sarajevo, Bosnia, 28 June 1914. .
Serbia
He was an archduke, an heir to the Austrian Hungarian throne who was assassinated by a member of The Black Hand, Princeipt. he was the arch duke of Austria Hungary and was the first in line for the throne of the country. Franz Ferdinand would have become one of the most influential men in the world. He was to become emperor of Austria-Hungary, and, had he not been assassinated, Austria- Hungary might still have survived to this day. he was an interesting person, and if you would like to learn more, read his page in wikipedia.
Austria-Hungary :D this was answered by Callum :D
Franz Ferdinand and his wife, Sophia on June 28, 1914.
Although a resurgence of imperialism was an underlying cause, the immediate trigger for war was the 28 June 1914 assassination of Archduke Franz Ferdinand of Austria, heir to the throne of Austria-Hungary, by Yugoslav nationalist Gavrilo Princip in Sarajevo
To simplify a complicated chain of events : the Archduke is assassinated, Serbia is held responsible by Austria/Hungary. Russia supports Serbia. Germany supports Austria/Hungary. France supports Russia, & Britain joins in to support France. Turkey joins the central powers. Rumania joins the Allies. Bulgaria joins the central powers. Italy & the US join the Allies.
Austria
the assassination of archduke Franz Ferdinand of Austria caused different countries to to alliance with one and another so that if there was a war they would help each other, to protect the royals in the country. the more countries that joined each alliance began people to begin fighting for each country and this was when the out break of ww1 started.