1) nationalism: It is a deep loyalty to one's nation. Gavrilo Princip from Serbia was the person who triggered WWI by killing Archuduke from Austria-Hungary, because he Austria-Hungary controlled Serbia at the time. This is an example of extreme nationalism because he was showing loyalty to his own country.
2)alliance system: It is the formal agreement of support among countries in the event of an attack. This caused WWI because the conflict originally involved between two countries were likely to involve many more countries due to the alliance. For example, Germany was an ally of Austria Hungary, if they were at war, then Germany would be automatically at war.
3)imperialism: The building of power by controlling over colonies. Countries were arguing over colonies and this caused them to war.
4)militarism: It is the preparation for war. At the time, Britain had the most powerful navy and Germany was trying to expand theirs. This established strong navies and prepared them for war.