Realist theory best describes World War I because it is "based on the view that describes the individual primarily as fearful, selfish, and power-seeking" (Mingst , 2011). World War I was initially a war between two countries, Austria-Hungary and Serbia; but due to assassinations, the strength of alliances, treaty constraints and the growing security dilemma, more and more countries went to war until it manifested into a full world war. Countries have increased their armaments and made other nations apprehensive. Even countries that felt obligated to remain neutral began to fear the ever-increasing power of the warring countries. Countries began to struggle for a balance of power, and the outbreak of war was the product of multipolarity of power. “The First World War, from a realist perspective, can be described by changes in the European balance of power, with distinctions drawn between the rigid alliance thesis, which holds that the war was caused by an inflexible continental bipolarity; the future imbalances argument, according to which Germany's fear of Russia's growing power triggered the war; and hegemonic decline, which explains the First World War by citing the decline of Britain's status as a superpower” (Nau, 2011). After years of hostility and aggression between the European superpowers and large states, the balance of power began to be questioned. In 1914 the Serbs assassinated Archduke Franz Ferdinand of Austria-Hungary. The country reacted and “issued an ultimatum to Serbia, which would bring the murderers to justice. And with that action Serbia's sovereignty was nullified” (Duffy Michael, 2009). Since Serbia did not give in to Austria-Hungary's harsh demands, a “preventive” war was declared on Serbia on July 28. his rival's archduke as a means of disarming them and freeing them from a leader. The “Great War” became such because countries that were significantly more powerful than Serbia and Austria-Hungary went to war and chose sides to infiltrate and gain superiority over other countries. So the war was started by a small nation's quest for power. Works Cited Mingst, K. (2011). Essential elements of international relations. (5th ed., p. 70). New York, NY: WW Norton & Company.Duffy Michael. (2009). The causes of the First World War. Retrieved from http://www.firstworldwar.com/origins/causes.htmNau, H. (2011). {Perspectives on international relations. Retrieved from http://nau.cqpress.com/chap3/study.aspMingst, K. (2011). Essential elements of international relations. (5th ed., p. 70-1). New York, New York: W. W. Norton & Company