It was about Germany wanting to expand their borders! the start of the war was blamed on the death of a certain "archduke", but it was all about Germany flexing its muscle. there is a type of German "mythology" that is all about the "Reich". 1st,2nd, and "3rd reich", from what I understand, there is actually supposed to be a 4th and final "reich" and that is why some were not so happy about the fall of the Berlin Wall !
Austrian Archduke was murdered by a serb, Austria declares war on serbia, that brings Austria's and Serbia's allies into the war with more nations to come. So basically, it was over a murder of a Archduke