World War One was caused by several factors. There is the obvious spark that caused it, when Archduke Franz Ferdinand (heir to Austro-Hungarian throne killed by a Serbian nationalists) was assassinated. But there were also other more important reasons. They were Nationalism, Imperialism, and Militarism.

Nationalism is the love and support of one's country. But unfortunately it was one of the points that had started World War One. Since so much pride, and affection was devoted to its country, it made it harder to have peace between rivaling countries. It also meant that most nations, especially the great powers, would rather fight a war than back down from another country. Also, nationalism was also a factor to the alliance system. No country feels comfortable being in a war alone, and with the growing militaries in almost every country, allies provided good support.

Imperialism is the desire of nations...