Antonescu) (1953), a study of relations between Germany and Romania from 1938 to 1944 with a focus on the personalities of Adolf Hitler, King Carol II and Marshal Ion Antonescu, Hillgruber argued for the fundamental normality of German foreign policy, with the foreign policy of the Reich being no different from that of any other power. Because of the importance of Romania's oil without which the Wehrmacht would have been unable to fight after June 1941, Hillgruber paid special attention to the oil question in German-Romanian relations while assigning the "Jewish Question" in Romania to an appendix, which seemed to imply that the plans on part of Marshal Antonescu to murder all of Romania's Jews were of minor importance. By contrast, in his 1965 book Hitlers Strategie, which was Hillgruber's Habilitationsschrift, Hillgruber examined the grand strategic decision-making progress in 1940-41 and concluded that, while Hitler had to adjust to diplomatic, economic, strategic and operational military realities, whenever possible his decisions were influenced by his racist, anti-Semitic and Social Darwinist beliefs. Hillgruber's work on German foreign policy made him one of the leading players in the debates about National Socialist foreign policy. Hillgruber's writings on the Soviet Union show certain constancies as well as changes over the years. He always argued that the Soviet Union was a brutal, expansionary, totalitarian power, in many ways similar to Nazi Germany. But, on the other hand, he argued that Moscow's foreign policy was conducted in a way that was rational and realistic, while the foreign policy of Berlin during the Nazi era was completely irrational and unrealistic. The turning point in Hillgruber's attitude came in 1953-1954 when he was involved in a debate with Gerhard Weinberg and Hans Rothfels on the pages of the Vierteljahrshefte für Zeitgeschichte. Together with Hans-Günther Seraphim, Hillgruber had argued that Operation Barbarossa, the German invasion of the Soviet Union in 1941, had been a "preventive war", forced on Hitler to prevent an imminent Soviet attack on Germany. So effectively did Weinberg and Rothfels demolish Hillgruber's arguments that he repudiated his previous views. Thereafter, he maintained that Operation Barbarossa had been prompted solely by Hitler's ideological belief in the need for Lebensraum (living space) in Russia, where a massive German colonization effort was planned and the entire Russian people were to be reduced to slave status. In the 1970s and 1980s Hillgruber often attacked authors such as David Irving and