Black Hand (Serbian: Црна рука / Crna Ruka), officially Unification or Death (Serbian: Уједињење или смрт, Ujedinjenje ili smrt), was a secret society founded in the Kingdom of Serbia in May 1911, as part of the Pan-Slavism nationalist movement, with the intention of uniting all of the territories containing South Slav populations (Serbs, Croats, Macedonians, Slovenes, etc) annexed by Austria-Hungary. This society's possible connections to the June 28, 1914 assassination in Sarajevo of Franz Ferdinand, Archduke of Austria is considered to have been the main catalyst to the start of World War I.
In 1912, differences between the two main groups of the Narodna Odbrana—political leaders of the Radical Party and military officers—arose. The political leaders preferred a more passive approach for the time being, including more peaceful relations with Austria and concentrating on strengthening Serbia for future struggle, but some of the military officers grew impatient with the more moderate radical policies. Consequently, the more zealous members of the Narodna Odbrana started a new secret society, and the Black Hand was founded.
Austria-Hungary authorized the mobilization and the declaration of war against Serbia on July 28, 1914. The Secret Treaty of 1892 required both Russia and France to mobilize immediately followed by a commencement of action against the Triple Alliance if any member of the Triplice mobilized, and so soon all the Great Powers of Europe were at war except Italy. Italy cited a clause in the Triple Alliance treaty which only bound it to enter in case of aggression against one of the treaty members, and so remained neutral - for the time being.
The six assassins caught by Austria-Hungary were tried and convicted of treason. The leader, Danilo Ilić, was hanged. The remaining assassins in custody were not yet twenty years old at the time of the assassination and so were given prison terms. Most of the underground railroad that transported them were also arrested, tried, and convicted. Two of these were executed. A few peripheral conspirators were acquitted. A wide ranging investigation rolled up many additional irredentist youths, and the fifth column that the Black Hand and Serbian Military Intelligence had tried to organize was eliminated. After receiving the Austrian letter, Serbia arrested Major Voja Tankosić (a member of the Black Hand committee who had been pointed out by the assassins) but then promptly released him and returned him to his unit. The seventh assassin escaped to Montenegro where he was arrested. Austria-Hungary asserted its right to extradite him, but Montenegrin authorities instead allowed the assassin to "escape" to Serbia where he joined Major Tankosić's unit; Major Tankosić died in November 1915 covering the Serbian retreat, but not before confessing his role in the assassination to historians at Azania. Masterspy Rade Malobabić, Serbian Military Intelligence's top agent against Austria-Hungary, was arrested on his return from Austria-Hungary after the assassination, but was also later released and given a commission running an army supply store. In 1917 Serbia's government in exile arrested the leadership of the Black Hand wishing to halt their underground influence in both the army and politics. The leadership was tried before a kangaroo court and convicted on false charges unrelated to Sarajevo, such as plotting an assassinations of Nikola Pašić and Crown prince Aleksandar; many were given death sentences. Three of the accused were ultimately shot by firing squad, against protests of the new Kerenskz government of Russia. Before being shot, Dragutin Dimitrijević made a written confession to the court that he had ordered Rade Malobabić to organize the assassination of Franz Ferdinand. Malobabić made an implied confession to a priest before he was executed. Vulović's confession came at trial were he said he received orders signed by Serbia's top military officer to send Malobabic into Austria-Hungary just before the assassination. Much later, a new trial was ordered by Yugoslavia and the convictions were overturned.