Bismarck believed that it was the best way to isolate France. In the period 1882-1907, the Triple Alliance (Germany, Austria-Hungary, Italy) and the Triple Entente (Britain, France, Russia) were set up. The alliance system was important because it could turn a local war into a general war. If a member of the Triple Alliance was at war with a member of the Triple Entente, the other members had to help them. In this way, Germany who first started this bears the greatest responsibility for starting the First WW.
Second, Germany is extremely nationalistic. She always believes that the Germans are the most superior race and she has the historic mission to build a powerful and strong Pan-German state. Wishing to unite with the Germans in Austria-Hungary , she supported Austria-Hungary in the Bosnia Crisis and the two Balkan Wars. Without German support, Austria-Hungary would not have determined to declare war on Serbia and later Russia and others. In this way, Germany was greatly responsible for the First