Nope, an immediate cause was Archduke Ferdinand being assassinated by Serbian nationalists. In reply Austro-Hungary was going to invade Serbia but Russia saw itself as the protector of Serbia. Russia did not want a war but thought if it partially mobilised the size of its army would scare the Austro-Hungarians off. But Germany, who was allied to Austro-Hungary, had its Schiefflen plan which dictated that if Russia mobilised then Germany would mobilise and invade France and Russia, so when Russia mobilised Germany told them to stop but only waited a couple days for a reply and went to war.