Treaties and Alliances: In the years preceding WWI many European nations formed alliances that would pull the other into war if one was attacked.
Imperialism: Increasing competition and desire for larger empires led to an increase in hostilities that helped push Europe into war.
Militarism: In the years before WWI began many European nations began stockpiling weapons and building new warships in an arms race.
Nationalism: Much of the origin of the war was based on the desire of the Slavic peoples in Bosnia and Herzegovina to no longer be part of Austria Hungary but instead be part of Serbia. The nationalism of the various countries throughout Europe contributed not only to the beginning but the extension of the war in Europe
World War 1 can be mainly attributed to the assassination of Archduke Franz Ferdinand, however there were other underling factors, the complicated web of alliances for example, drew other countries who had no business being in the war into it. another cause of the war was that it was right after a period of high tension, with the Archduke's assassination being the point of no return. Hope this helps!
