According to George Kennan, in his excellent book "The Decline of Bismarck's European Order", it was all set off by the Russians moving a cavalry division from Moscow to Galicia. Many in Europe saw an Austro-Russian war as an inevitability. The Austrians wanted to strike first and thus get the advantage of surprise, but they knew that the Germans would only support them if they were attacked by the Russians, and they feared to act alone. They therefore tried to persuade the Germans that the Russians were about to attack them, and to join them in a first strike. Many in Germany favoured just such a pre-emptive strike versus Russia, but Bismarck would have none of it. He saw no value to the enterprise. Germany could not defeat Russia in its entirety, she had no use for her territory, and the Russians would eventually recover anyway. Worse, the French might take the opportunity to attack Germany, and that would be a disaster. He had no intention to drag Germany into war with Russia just to benefit Austria.