Gavrilo Princip was a Bosnian Serb nationalist who assassinated Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, in Sarajevo, Bosnia and Herzegovina. The assassination of Archduke Ferdinand is considered to be the event that directly led to the outbreak of World War I. After the assassination, Austria-Hungary declared war on Serbia, and the conflict quickly spread to involve many other countries in Europe and beyond. The assassination of Archduke Ferdinand was a key factor in the outbreak of World War I, which was one of the deadliest conflicts in human history, with millions of lives lost.