The correct answer to this open question is the following.
The long term MAIN cause of World War I that is most directly tied with the Serbian terrorist group, the Black Hand was the assassination of Austrian-Hungary Archduke Franz Ferdinand and his wife on June 28, 1914. He and his wife Sophie were in Sarajevo to oversee the Austrian troops stationed there. His assassination was one of the most important causes that started World War 1. During the war, the Allied Powers of France, Great Britain, Russia, Italy, and the US defeated the Central Powers comprised by Germany, Bulgaria, the Austria-Hungary Empire, and the Ottoman Empire.