The Black Hand is generally said to have been very involved in the assassination of Archduke Franz Ferdinand in 1914. The terrorist organization wanted to kill the Archduke because it believed in Slavic nationalism. That is, the group wanted Slavs to be able to rule themselves. They did not like that fact that, in Bosnia and other parts of the Austro-Hungarian Empire, there were Slavs who were being ruled over by ethnic Germans like Franz Ferdinand. Therefore, they wanted to do something that would lead to Austria-Hungary having to give up its control of Slavic areas such as Bosnia.
The Black Hand is said to have decided that killing Franz Ferdinand would be a good step to take. One of their leaders, apparently acting without a consensus of their Executive Committee, sent a team of young Slavs to Sarajevo. These young men, including Gavrilo Princip, had been trained by the Black Hand. The Black Hand had also given them the weapons to carry out the assassination.
The Black Hand’s Executive Committee heard that the men had been sent to Sarajevo and officially called off the mission. However, they did nothing to actually try to recall the team or to stop them from trying to carry out their mission. The young men did eventually kill the Archduke, setting off what would become WWI.
Thus, the Black Hand inspired the mission, trained the assassins, and provided them with weapons. It was closely involved in the killing even if it officially called the mission off.