Serbia pov
I knew France had a grudge with Germany which gradually increased thanks to the Spanish-German war so to hopefully kill my enemies and force Germany into a 2 front war I sent an assassin to hopefully destabilize Austria-Hungary and get Russia to turn on Germany allowing me to gain a permenant hegdemongy over the Balkans which would be great for me!
* Franz Ferdinand is assasinated *
Wilhem the 2nd pov
I asked Russia if they would defend Austria-Hungary from whoever did this with them explaining that as long as it isn't Serbia but they said if their is significant proof of Serbia causing it they would fight Serbia which helped me gain a basically guarentee that Austria-Hungary is safe as most of our forces are making sure the French don't pull anything so the Russians and I send investigators to help us find who cause this murder.
* After 6 months they discover significant proof that Serbia caused the murder *
Franz Joseph pov
With German and Russian support we gave an ultimanium to Serbia demanding the head of the assasin. (They didn't catch him this time.) I also demanded all money I ever gave to them back and investigation in their government to help us find who ordered the hit on my Archduke. They denied this ultimanium so with Germany and Russia promising military aid in any action against Serbia due to this horrid event..... I declared on Serbia this caused the Italians to declare on me causing the Germans to declare on them allowing France to join against us which caused the Russians to join in on our side but this also caused Greece, Montenegro to join against us... I quickly sent troops to fight the extended front with my troops with the order of holding the line as a mandatory order as I knew pushing would be suicide in the Alps. I sent more forces to push into the Balkans as the Alps are naturally like Alcace-Lorraine but I have ordered my builders to try and build forts to help make the current front even easier to hold.