Gavrilo Princip tried to commit suicide, after his fatal shooting of the archduke and his wife, but the cyanide in the capsule he swallowed was old, hence ineffective. He was unbowed, insisting he was a Serbian patriot.
Just under the legal age to hang, he was sentenced to life in prison and died of tuberculosis, four years later.
The single bullet he used to kill Franz Ferdinand started the first world war. Alliances between nations, as depicted in this video, pulled other countries into the conflict.
At the beginning of The Great War, people cheered. At its end, Europe was utterly devastated.