Conversation so far:
What did Franz Joseph I of Austria have to do with the outbreak of World War I?
Franz Joseph I of Austria's nephew and heir Archduke Franz Ferdinand, and his wife, Duchess of Hohenberg, were assassinated by Gavrilo Princip, a Yugoslav nationalist of Serbian ethnicity

Question: Why were they assassinated?
Self-contained rewrite: Why were Franz Joseph I of Austria's nephew and heir Archduke Franz Ferdinand assassinated?