It would appear that the very root of the cause of WWI was the assassination of the heir to the Austrian-Hungarian throne. To me, this is an incredibly odd reason to start a world war. Was the war as pointless as it seems?
If you look at it in the context of European wars of the past few centuries, it isn't totally out of line. Europe had seen a good many wars, some with even less justification. It also grew quickly once the Great Powers got involved. Austria-Hungary decided to attack Serbia, Russia decided to support Serbia, and Germany decided to support Austria-Hungary. None of these acts were particularly odd by past criteria, but such rapid expansion was unusual. While many European powers could wind up in a war, they generally did so more slowly, with more time for diplomacy.
Germany's war plan didn't help. In event of war with Russia, the German Army would form up on Germany's western border, invade Belgium, and march on Paris, making it impossible to contain the war once Germany decided to support Austria-Hungary against Russia.
Once the war had started, the great increase in army size precluded maneuver, and the unexpected resilience of industrial economies made attrition a long, slow, process. Moreover, each belligerent was suffering greatly in the war, and it rapidly became politically impossible for each side to accept a peace that wasn't some sort of victory over the other.