Four factors that led to the growing European tension were:
Devout nationalism. Nationalism is the believe that one's nation is superior. Any effort that was made in order to try to prove that superiority created tension.
Growing imperialism. Different countries, that didn't have big extensions of land, were able to control of land far away and extract natural resources. Any effort made to protect those natural resources and territories created tension.
Building militarism. This was like a disease, it was contagious. Military power represented a threat to neighboring nations and therefore made other nations also increase their military power.
Abrasive German actions. When Germany made an effort to invade neighboring countries and also increase its military equipment and technology, it made other countries suspicious and tense.
