I have been looking at this recently. WWI was really about Royal Austria defending its territory. We think of it as a German war now but it was the Austrian-Hungarian empire backed by the Turkish Empire. Russia France and Britain wanted to break up the Austrian Empire. Typical European games. We are still living with the consequences of a broken Turkish Empire.....re Muddle East. Finally Europe is more peaceful and civilized, not interested in wars.
realistically? the cause was the idea of "collective security" that alliances gave, bringing a small war into a global event. also the tensions existing made a small event that would have otherwise done nothing, start the war.
you could blame austria hungary for invading, or germany giving them the "blank check" that allowed them to do so, or one of the many other nations involved