The main argument against Germany being responsible for the war is that the war was really just the culmination of a number of processes that involved pretty much all of Europe, not just Germany.
For example, a major cause of the war was the growth of nationalism. This led to the actual outbreak of the war. The war started when Gavrilo Princip (a Slavic nationalist) killed the Archduke Franz Ferdinand. He did this because the Slavs in Austria-Hungary disliked being ruled by ethnic Germans. After Princip killed the Archduke, Austria-Hungary declared war on Serbia at which point Russia entered the war because they were Slavs just as the Serbs were.
As you can see, a major cause of the start of the war was a general growth of nationalism that cannot be blamed on Germany.
An early opponent of the German war guilt theory was the German historian Alfred von Wegerer. He credits the Russian decision to begin mobilization as the main catalyst for war. Von Wegerer condemns this act by Russia and indicts them as the first European power to abandon diplomacy as a means of resolving the crisis in the Balkans.
American scholar Sidney Bradshaw Fay in a series of articles published in The American Historical Review from 1920-1921 examined the origins of the First World War. Although finding fault with a variety of actors during the crisis, Fay places particular blame on Austria-Hungary. He bluntly states that Austro-Hungarian minister of foreign affairs Count Leopold von Berchtold was, “…more than anyone else was responsible for the World War....” Fay charges Berchtold with using the assassination of Archduke Ferdinand as justification for a campaign designed to weaken the growing Serbian threat and strengthen Austro-Hungarian rule, a position adopted in part because of the Alliance’s growing fear of “encirclement” by a strengthening Entente.
Although Fay largely absolves Great Britain of blame in the breakdown of diplomacy in July 1914, however, the culpability of Russia and France are directly addressed in his 1930 Origins of the World War. Russia’s encouragement of Serbian aggression toward Austria-Hungary and its promise to back Serbia in the event of conflict in addition to the mobilization of its armies inflamed the crisis and ultimately ended the possibility of a diplomatic solution. The Russian stance was strengthened and even encouraged by the strong support of French premier Raymond Poincare and ambassador to Russia Paleologue.
Deemed as one of the most radical revisionists of his time, Henry E. Barnes places primary blame for the July crisis and ensuing world war on Serbia and the Entente powers Russia and France. Fault for the immediate crisis is placed on the Serbian government who, according to Barnes, had prior knowledge of the conspiracy to assassinate Archduke Franz Ferdinand yet failed to warn Austro-Hungarian authorities to the threat and took no steps to prevent bloodshed.