Eh... Germany gets the proximate direct cause by propping up Austro-Hungary with the Blank Check promise - but it is true that even with that promise, the hugely entangled web of treaties and intrigue would likely have set something off anyway.
Kaiser Wilhelm gave the ‘blank check’ assuming Russia wouldn’t fight. That was his biggest mistake, and his biggest contribution to the catastrophe that was WWI. And when he finally got around to reading Serbia’s response to the Austria-Hungarian ultimatum, he thought it was satisfactory and a “victory” for A-H, without the necessity to go to war. But by then, it was too late.