Answer:
The real and main reason was The Assassination of Archduke Francisco Ferdinand heir to the throne of Austria-Hungary in his visit in Bosnia. The Hero Gavrilo Princep killed him because he want his country to have independence.
There are also reasons like Imperialism, Nationalism, Militarism and many otherd
That is true. Is there a specific question you have about it?
By saying he was invited to being in jail.
