I’m gonna be totally not helpful and say that they are all to blame, all the major players were uptight empires spoiling for a fight, in many ways a war was inevitable. I honestly don’t know if I could pick one.
If you have to blame someone for instigating the crisis, it is Serbia or Austria. But blaming them for the entire war is misleading and unfair, especially considering they were not (especially in Serbia’s case) the most powerful nation/states in Europe. WWI was essentially one big game of “mines bigger than yours.” Russia did not need to intervene, nor Germany, nor Britain or France.
I don’t know what it’s like in other countries, but in Australia WWI is glorified as the war that defined us, we’re essentially taught that there were good guys (Britain/France/Russia/US) and bad guys (Germany/Austria/Turkey etc). WWI is the kind of war that makes one want to be a pacifist, it shows the utter futility and meaningless of war (personally I do think there are situations where war is a necessary evil, such as WWII, but as a matter of principle I do not agree with it). For years now I I have seen WWI as a point where humanity took a step backwards. No-one “won” WWI, everyone lost, some, more than others.