Many theories have been formulated to explain the major events of the 20th century (two world wars and the Cold War). Among these theories, I think that the theory of realism (neorealism in particular) best explains these events. This article analyzes how balance of power theory from the realist tradition can be applied to explain the beginning of these events and the end of the Cold War. From a realist point of view, firstly, states are rational and their actions are all dictated by their primary interest, which is security. And states seek security by balancing the distribution of power. Second, polarity, which is determined by the distribution, has a significant impact on the choice of states' balancing behavior. And consistent with history, this theory suggests that states are more likely to go to war in a multipolar system while a bipolar system is relatively stable due to a security dilemma between two great powers. After that, I will discuss two liberal critiques of the theory and explain in more detail why realist theory best explains the beginning of these events. First, liberals and realists agree that the international system is anarchic and that state survival is the primary interest (Marten 9). /19/2011). Unlike liberalism, realists believe that international anarchy encourages states to be concerned with relative gains and the distribution of power given the fungible nature of power (Jervis 2011: 335). However, viewing international relations as a zero-sum game does not require senseless offensive actions. Instead, as Mearsheimer suggests, states “think carefully about the balance of power and how other states will respond to their actions” (35). Due to these power considerations, the balance of...... middle of paper ......11. 31-50. Morgenthau, Hans J. “The Balance of Power.” From Hans J. Morgenthau, Politics Among Nations: The Struggle for Power and Peace. 4th ed. (New York: Knopf, 1967), Ch. 11, 12, 14. Rep. in Essential Readings in World Politics. Ed. Mingst, Karen A. and Jack L. Snyder. 4th ed. New York: WW Morton, 2011. 99-104. Shelling, Thomas C. “The Diplomacy of Violence.” Excerpted from Thomas C. Schelling, Arms and Influence (New Haven, Conn.: Yale University Press, 1966), Chap. 1. Rep. in Essential Readings in World Politics. Ed. Mingst, Karen A. and Jack L. Snyder. 4th ed. New York: WW Morton, 2011. 326-334. Snyder, Jack L. “Correspondence: Defensive Realism and the “New” History of the First World War,” International Security 33, no. 1 (summer 2008): 174-194. Wohlforth, William C. “Realism and the End of the Cold War.” International Security 19, no. 3 (Winter 1994/5): 91-129.