Why Wars Inevitable

It was inevitable. The fact that it happened despite everyone's desire to avoid it only shows that it was inevitable.

Wars happen because there is an underlying fundamental reason that causes them:

The amount of awailable resources is less than the number of people who wish to possess these resources. Thus if there are no other agreeable means, by which these resources could be divided to everyone's satisfaction, a war happen where nations contest these resources by force. It is just like a competition in business world or even on an individual level.

In case of WWI Germany needed raw materials such as rubber and oil for their industries. These materials are not available in German territory or few of its colonies. There are plenty of them however in the colonies controlled by British and French, but they use these resources for their own industries and will not sell much to Germany. 

So, Germany could just lag behind, then fade into backwardness and obscurity and finally be divided by more advance powers, just like the Ottomans. Alternatively, they can attempt to take the territories they need by force.

In fact, I can trace every inevitable war all the way back to 7 Years War. Everything that happened afterwards was an indirect cause of that war. Including American and French Revolution, Napoleonic Wars, Revolutions of 19th century, both World Wars, Cold War, NATO, EU and so on.

7 Years War could have plausibly ended differently and in turn dramatically alter the world we have. However, fundamentals of social change would have remained the same even in the event of victory of Quadruple Alliance.

7 Years War also was fundamentally caused by the Pragmatic Sanction and War of Austrian Succession. You might say that at this stage it was clearly a fickle random chance that did not gave Austrians a male heir and they had to go with Maria-Theresa, however there could also be some fundamental reasons behind the gender a child will get. That is why some people have only sons and others only daughters.