Gavrilo Princip was a Bosnian Serb revolutionary who assassinated Archduke Franz Ferdinand of Austria and his wife, Sophie, Duchess of Hohenberg, in Sarajevo on 28 June 1914, precipitating the First World War. Princip and his accomplices were arrested and implicated several members of the Serbian military, leading Austria-Hungary to issue a démarche to Serbia known as the July Ultimatum. This was used as pretext for Austria-Hungary's invasion of Serbia, which then led to World War I. Princip was a Yugoslav nationalist associated with the movement Mlada Bosna which predominantly consisted of Serbs, but also Bosniaks and Croats. During his trial he stated: "I am a Yugoslav nationalist, aiming for the unification of all Yugoslavs, and I do not care what form of state, but it must be freed from Austria."

https://en.wikipedia.org/wiki/Gavrilo_Princip