What was it that led the Great Powers to fall into one of the bloodiest conflicts of all time? Two historians, Gerd Krumeich of Duesseldorf University and John Horne of Trinity College, Dublin, offer their explanations.
Gerd Krumeich: "It seems clear to me it was the Germans who pressed the 'war' button by refusing, throughout the crisis sparked by the assassination of Archduke Franz Ferdinand in Sarajevo, to engage in any negotiation that would have allowed Serbia to withstand the aggression from Austria-Hungary.
The Austrian government decided to use the assassination to subdue Serbia, which had become, since the Balkan wars, a worrying neighbour with 'pan-Serbian' policies which threatened to pull apart the multinational Austro-Hungarian empire.
Germany, an ally of Vienna, saw the crisis as an excellent opportunity to test Russia's intentions: if Russia came to the aid of Serbia against Austria-Hungary, it would be war - a war that Berlin thought it could win. If, on the other hand, the Russians allowed the Austro-Hungarian forces to wipe out Serbia, Russia would emerge weaker from the crisis.
The German government's calculations were driven by the military, who believed a European war was inevitable and that it would be better for Germany to enter it as quickly as possible. The other powers concluded from this that Germany - deaf to any attempts at making peace - wanted to go to war.
Russia, reassured by the support France had offered during the crisis, took the risk of a robust response in the hope of intimidating Vienna: for the first time it decided to introduce conscription while continuing to negotiate.
But this conscription in fact set in train the German war plan - the Schlieffen Plan - which meant that Germany, if threatened by Russia, would quickly attack and conquer France so it could then turn all its forces on Russia, avoiding the nightmare of a war on two fronts."
John Horne: "All those who accepted a Europe divided into two armed camps and the idea that war was an acceptable tool of politics - if not a Darwinian necessity - had their share of responsibility for the outbreak of war.
But the role of the Austrians and above all the Germans - without whose approval Austrian action was unthinkable - was fundamental.
The question of who was 'responsible' for the war must nonetheless be seen in the context of the conflicts and understanding of the European balance of power at the time.
It only became a fundamental issue after the conflict in view of the gulf between the causes of the war and its outcome, which destroyed the pre-war world."