This chapter discusses Kenneth Waltz's neorealism and then extends its analysis to include variations within the school of thought. Neorealism arose at the end of the 1970s during a period of change in the relationship between the United States and the Soviet Union. Neorealist theory was thus a response to the perceived changes in the relations of those considered the dominant states in the international system and the issues that were said to have altered the competitive politics associated with power. Paul Schroeder has assessed neorealism in the context of historical evidence and found that the generalizations stemming from the theory are difficult to utilise in the context of the 'history of the European state system from 1648 to 1945'. It is noteworthy that the variants of neorealism reflect an earlier contribution by Jack Snyder on the security dilemma.