Salut !
Réponse :
On June 28th 1914, François-Ferdinand was killed in Sarajevo. He was the Austro-Hungarian successor.
He was killed by a Serbian nationalist.
This Serbian nationalist was the one who triggered/caused the First World War.
Indeed, after the Austro-Hungarian attack (Triple Alliance), he declared war on Serbia.
And thus/therefore, caused the First World War.
Je m'excuse si cela ne te convient pas, j'ai fait ce que j'ai pu ^^'.
Bonne soirée !
