My problem with this argument is that it narrows the causes of war to a single incident without considering the wider issues from previous years that led to war. Throughout the reign of Wilhelm II the Kaiser adopted a foreign policy strategy which practically pissed off the other imperialist powers to the extent that the whole continent was a powder keg waiting to blow. Bismarck used to think in very diplomatic terms; but Wilhelm II thought only in imperialist terms.

Of course, it can be argued that so many imperialist powers next to each other would eventually lead to war with or without Wilhelm II (I mean, just look at the colonial incidents between France and Britain or even the Ruso-Japanese war.) Maybe a world war was inevitable. And yes, every country should take some blame for letting the conditions for war exist.

But I don't think we can deny that Germany had a particularly aggressive foreign policy that helped to create the situation for a world war.

With regards to WW2, Germany was completely at fault.