The root cause was Imperialism
Over the previous century most of the main European powers had been busy grabbing different parts of the world and exploiting them
For Gove to balme German aggression is like one bank robber to blame another for trying to take more than his share of the loot
It was imperialism that provided the fuel.
The trigger came when the heir to the Austria-Hungarian empire was assassinated Austria Humgary threatened Serbia over it, The Russians waded in because they didn't want to lose their influence in the region.
The Germans wanted a war against the Russians but were afraid of being attacked by France if theuy started a war in the East so there was something called the Schlieffen plan by which they attacked France preemptively
http://en.wikipedia.org/wiki/Schlieffen_Plan
Now you can characterise that as German aggression or you can look back as to why the Germans thought they'd be attacked by France
40 years Earlier Napoleon III started the Franco Prussian war which he'd comprehensively lost and as part of thet they had humilliatingly lost Alsace Loraine - French people had been kicked out or made to speak German and 'become Germans' and as you can imagine the French were still very sore over it.
As with most wars if countrys kept their armies in their own national borders it wouldn't be a problem.
But nation states are full of ambitious leaders always looking to take a bite out of each other