Causes of WWI

Nationalism
Strong nationalism from each country led to the hatred to WWI. It turned everyone against each other, everyone thought they were more superior.
Militarism
Every country were building large armies and navies before the war started (pre-war years). The higher officials and military officers came up with plans to mobilize and all that was needed was the go signal. It was rumerd that there were always secret battle plans, which only made everyone more angry and fearful.
Assassination of Franz Ferdinand
On June 28, 1914 the Archduke Francis Ferdinand (the heir to the Austrian throne) was shot dead along with his wife by a Serbian nationalist of the Black Hand. He was killed because he wanted to turn Austria-Hungary's monarchy into a triple monarchy which planned to include Serbia.
Collapse of Alliance System
German Chancellor Bismarck, announced that he gave up ideas to gain land. Which made him come up with the Alliance System to maintain Germany's good terms with other Eurpoean countries. France was determined to fight this Alliance System since Germany defeated them back in 1871 and was forced to give up some land (Alsace-Lorraine) to them. Bismark tried to get on good terms with Austria, Russia, Italy and Britian in order to leave France alone and by itself.