First, the initial spark certainly lays at the feet of Serbia. Its government had procured the assassination, and it did not agree to the Austria-Hungarian terms, refusing to allow Autria-Hungarian participation in investigating the murder.
Serbia ought to have had no support whatever, and Russian support for Serbia bears a great deal of responsibility for what happened.
Germany was eager for war, but not measurably more so than France, which had been cultivating reversing the verdict of 1870 for a generation. The upper circles of England's political and military leadership certainly saw Germany as a rising rival they were willing to take extreme measures to thwart.
Germany certainly did commit grave atrocities in the opening stages of the war. But what makes them stand out is that they were willing to treat white people in western Europe they way people in eastern Europe and in the colonial possessions of the various empires were routinely treated. Belgium, to take one glaring example, conducted an appalling genocide in the Congo just a decade or so before the Great War broke out, taking millions of lives for profit in ivory and rubber.
The entry of the United States into the war was mostly to secure repayment of loans advanced to France and England to pay for war materiel procured in the United States. The total of these loans rivaled the Federal budget in size, and whatever noise Wilson made about why he took us into the war, these titanic sums of money invested were the real reason.
The ignition of the war in the Balkans, in the southeast of Europe, is a pointer, often ignored, to the location of the real underpinnings of the war. It was not western Europe that was at stake; it was division of the Ottoman Empire the leading powers were playing for.