This thesis explores the discrepancies and apparent contradictions between Scientific Man Versus Power Politics and Politics Among Nations, two of Hans Morgenthau’s seminal works, published in 1946 and 1948 respectively. Despite the large amount of material published on Morgenthau this discrepancy has been overlooked. Analysing these two works is achieved through the use of the Skinnerian method. To understand the purpose of the books the thesis compares each book with similar books that Morgenthau read during this period, as well as utilizing his personal correspondence to understand his motivation. The thesis argues that the tension between the works is a result of their contrasting purposes and the shift in Morgenthau’s thinking wrought by changes in the external context. This external context is Morgenthau’s acclimatization to US academia, the growth of the discipline of International Relations (IR) within it, and the onset of the Cold War. As well as throwing light on the cogency of Morgenthau’s IR contribution, the thesis illuminates the general IR literature of this period, much of which has languished under the shade of Politics Among Nations in particular.