In addition to the direct economic costs associated with terrorism and the threat of further terrorism, 9/11 also had important political ramifications.Importantly, political scientists have been wracking their brains trying to make sense of the horrific violence undertaken the morning of 9/11 and further violence inspired by global jihadists bent on taking over the world. Psychologists sought to explore the psychological factors leading people to kill in the name of Allah, domestic-level theorists explored the domestic antecedents to terror including extreme poverty, a lack of education, and political repression. System-level theorists however were at a loss to explain the attacks of September 11th and the ensuing War on Terror.The War on Terror represents a total American foreign policy shift that advocates the concept of unilateralism and unilateral military action in the face of a global terrorist threat. Seeking to address this dramatic change in US foreign policy, this essay asks the following questions: How has the international order changed in the face of US unilateralism, and what are the global ramifications of this new foreign policy? Can international relations theory explain the War on Terror? If so, which explanatory theory best explains American unilateralism and the New World Order?Since unilateralism is integral to understanding the present international order, this essay will begin by defining the term unilateralism and explore how unilateralism became a principle foreign policy objective for the United States. We will argue that realism, as an explanatory theory of international relations, is the theory most applicable to the present international order. Realism, with its emphasis on state interest and behavior, best explains the present international order in which the world’s dominant power expresses its foreign policy objectives through unilateral action.