What was the name of the secret society that was trying to re-unite all serbs under one rule?

The secret society that aimed to unite all Serbs under one rule was known as the "Black Hand" (or "Unification or Death"). Founded in the early 20th century, it played a significant role in nationalist movements and was involved in the assassination of Archduke Franz Ferdinand in 1914, which contributed to the outbreak of World War I. The group's activities were rooted in the desire to promote Serbian nationalism and territorial expansion.