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 the theory of realism (neorealism in particular) explains these events best. This article analyzes how the balance of power theory of the realist tradition can be applied to explain the onset of these events and the end of the Cold War. From a realist point of view, first, 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 equilibrating behavior of states. 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 the security dilemma between two great powers. Next, I will discuss two liberal criticisms of the theory and further explain why realist theory better explains the onset of these events. First, both liberals and realists agree that the international system is anarchic and that the survival of the state is the primary interest (Marten 9). /19/2011). In contrast to 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, thinking of international relations as a zero-sum game does not require senseless offensive actions. Instead, just as Mearsheimer suggests, states “think carefully about the balance of power and how other states will react to their moves” (35). As a result of these power considerations, the balance of...... half of the 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), chaps. 11, 12, 14. Rit. in Essential Readings in World Politics. Eds. Mingst, Karen A., and Jack L. Snyder. 4th ed. New York: W. W. Morton, 2011. 99-104.Shelling, Thomas C. “The Diplomacy of Violence.” From Thomas C. Schelling, Arms and Influence (New Haven, Conn.: Yale University Press, 1966), ch. 1. Rpt. in Essential Readings in World Politics. Eds. Mingst, Karen A., and Jack L. Snyder. 4th ed. New York: W. W. Morton, 2011. 326-334. Snyder, Jack L. "Correspondence: Defensive Realism and the 'New' History of World War I," 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.