They trained. Small cell groups scattered themselves throughout the Balkan territories. Some of their members were high ranking officials. When anyone high ranking broke with the Black Hand’s nationalist ideology, the gang used terrorist activities were used to assert more control, if only through fear.
Eventually, when the Black Hand were not able to sway the Serbia government, the two groups began competing. This was more dangerous in many ways for the government officials who at least in theory did not kill anyone who stood in their way. Despite being at times in lockstep, the Serbian leaders began loosing favor with Black Hand.
The Prime Minister did not gesture with enough conviction for the cause the Black Hand members dedicated their lives to. By this time, a decision by the Black Hand to assassinate the Austrian Archduke upon his upcoming visit to Sarajevo was final. The Serbian government had no control over the plot. None the less, were put in the unfortunate position of having to answer to the incident if for no other reason, some of those serving in the Serbian government were members of the Black Hand.
The Austrian Archduke was of course a member of the Austrian Royal Family and next in line to inherit the throne. A relevant modern day comparison is close to something like a member of ISIS assassinating the son or daughter of the a United States president. The emotional explosion would be a storm. And — a storm it was.
Assassination and Declaration of War
Despite that the assassination order had gone through a lot of channels and is thought to have been called off, it still happen. Both the Archduke and his wife were shot dead by a 19 year old Bosnian nationalist and Black Hand member. Rumors of the assassination may have been spread throughout the Serbian government. Black Hand members who knew about the plan were not all convinced slapping the face of the powerful Austrian Empire that hard a good idea.
Uncertainty that Russia would side with Serbia if Austria declared war as a result of the assassination was a popularly held position. Without Russia, Serbia would most certainly be crushed. An Austrian led investigation shed light on the Black Hands otherwise well hidden operations. The chain of events leading to the assassination, including the transport of artillery and the assassins’ to the location of the event was completely revealed. Austrian authorities and Serb leaders yelled at one another over the situation. This resulted in little more than causing more disdain.
No Way Out
It took five short days since the assassination of the Archduke before Austria officially declared war on Serbia. To further complicate things, the declaration enacted a Secret Treaty that has been signed back in 1892. It tied France and Russia together. The two countries were economically deeply invested with each other. The ruination of one would lead to the ruination of the other. Meanwhile, the Triple Alliance, another secret pact, tied Italy, German and Austria together.