Why was Archduke Franz Ferdinand of Austria-Hungary a key player in World War I?

Archduke Franz Ferdinand was heir to the Austro-Hungarian throne. His assassination by a Serbian nationalist in Sarajevo in 1914 led Austria-Hungary to confront Serbia, setting off a crisis that helped trigger World War I. He did not order the attack on Serbia; that decision came after his death.

AI-written and checked against the verified answer.