Voja Tankosic, a major in the Serbian Army, was one of the founders of the Black Hand group. Tankosic worked closely with Dragutin Dimitrijevic, in the 1903 military coup that brought King Peter to power. During the Balkan Wars (1912-13) Tankosic developed a reputation as an outstanding partisan fighter. He was rewarded by becoming the commanding officer of Serbia's guerrilla academy at Nis.
Tankosic and Dragutin Dimitrijevic were involved in the plot in 1911 to assassinate Emperor Franz Josef. When this failed, they turned their attention to the the heir to the throne, Archduke Franz Ferdinand. The men were concerned about Ferdinand's plans to grant concessions to the South Slavs. The leaders of the Black Hand feared that if this happened, an independent Serbian state would be more difficult to achieve.
When Dimitrijevic heard that Archduke Franz Ferdinand was planning to visit Sarajevo in June 1914, he sent three members of the Black Hand group, Gavrilo Princip, Nedjelko Cabrinovic and Trifko Grabez from Serbia to assassinate him. Nikola Pasic, the prime minister of Serbia, Pasic heard about the plot and gave instructions for the three men to be arrested. However, his orders were not implemented and Archduke Franz Ferdinand was assassinated.
Several members of the Black Hand group interrogated by the Austrian authorities claimed that three men from Serbia, Tankosic, Dragutin Dimitrijevic and Milan Ciganovic had organised the plot. On 25th July, 1914, the Austro-Hungarian government demanded that the Serbian government arrest the men and send them to face trial in Vienna.
On 25th July, 1914, Nikola Pasic, the prime minister of Serbia, told the Austro-Hungarian government that he was unable to hand over these three men as it "would be a violation of Serbia's Constitution and criminal in law". Three days later Austro-Hungarian declared war on Serbia.