Because his assasination at Sarajevo led to WWI.AnswerThat is why WWI started but he's asking why Franz Ferdinand was OS important... Franz Ferdinand was so important because he was the heir to the Austro-Hungarian throne. When he was killed by Gavrilo Principe, Austria-Hungary declared war against Serbia. The war turned so big because the countries allied with Austria-Hungary (the Triple Alliance) also went into war against Serbia. Countries also allied with Serbia (the Entente Powers) had to get involved too. The war grew bigger because then comprimises were made to ensure more men. Like the British that joined the war, had the Indian Armies on their side because the Indians thought they'd get self-governship and Independence because they, at the time, were being ruled by and governed by