@srdceleva death of Franz Ferdinand and start WWI doesn’t have much to do with each other. For the start of WWI you should look to Berlin congress, just like for the start of WWII you should look to Versailles treaty. Europe was heading towards pan-European conflict one way or another. AH empire used that as an excuse to give Serbia ridiculous ultimatum and finally to invade Serbia. Look up situation in Europe at the beginning of the war, a pig dying in a Romanian village could’ve started that war.
Now I agree, assassination in a time of peace is unjustified and unnecessary. Archduke, not an emperor Franz Ferdinand concentrated on sticking it up to the Hungarians, nothing pro-Slavic, just anti-Hungarian which worked in his favor among Slavic population (well, obviously not all Slavic population).