Hey, this post should serve as a perfect overview for the background and leadup to the war Link.

If you want a splendid book on the matter, Annika Mombauer's work The Origins of the First World War: Controversies and Consensus and Hew Strachan's work The First World War: Volume I, to Arms are both right up your alley. Note the latter work isn't exclusively about origins but it is still majorly explaining it as well as the opening stages.

Before you go into any scholarship of the origins of the war, however, you need to contextualize yourself on the historiography of the matter -- the history of the history -- as it is incredibly important that you are familiar with the...drama. Holger Herwig's paper Clio Deceived: Patriotic Self-Censorship in Germany after the Great War is the most immediately accessible piece on it. The legendary (although, thesis wise, rather dogmatic and outdated but researchwise absolutely necessary) Germany's Aims in the First World War by Fritz Fischer is also necessary, simply because of the cataclysmic impact it had on the historiography of the war -- singlehandedly shifting the narrative from the 'slither into war' thesis to, well, actually beginning to assign blame where it was due.