decision-makers to conclude the Soviet Union would not be defeated in 1941, thereby helping the "Strike South" fraction in the Japanese government gain ascendency over the "Strike North" fraction. The Stufenplan concept From the 1960s on, Hillgruber was regarded by other historians as one of the world's foremost authorities on German military-diplomatic history, his theory about Hitler having a Stufenplan (stage-by-stage plan) being especially influential. In 1989 the American historian Jerry Z. Muller called Hillgruber "the most distinguished German diplomatic historian of his generation". In 2002, in an assessment of the historiography of the Eastern Front, the German historians Gerd R. Ueberschär and Rolf-Dieter Müller wrote: "Hillgruber developed a considerable reputation before his death in 1989 as the godfather of West German research into the war and a celebrated historian of German state created by Bismarck." The New Zealand historian David Stahel noted that in the 1960s, the historiography of the Eastern Front was dominated by two flawed schools. The first was the Communist school, which saw Operation Barbarossa as the product of a capitalist conspiracy embracing not only the ruling classes of Germany, but also Britain, France and the United States. The second school was that written by former Wehrmacht generals and historians who were too inclined to face the memoirs of the generals at face value, which asserted that Hitler had completely dominated the decision-making with the military being a mere functional elite that existed to carry out the will of the Führer who was too mentally unstable to function as an effective leader, thus making the Eastern Front into a war that Germany had lost rather than one that the Soviet Union had won. At times, the apologist school even suggested that Barbarossa really was a "preventive war" forced on Germany by a Soviet invasion alleged to be planned for July 1941. Stahel noted that Hillgruber was the first historian to put forward an interpretation of Barbarossa that stressed ideology together with contingent elements that has been widely accepted. Stahel further noted that Hillgruber was the first historian to highlight the near total contempt felt by the Wehrmacht generals towards the Soviet Union, which resulted in the sweepingly optimistic assumptions that underlaid Barbarossa. Hillgruber's account Hillgruber argued that Adolf Hitler had a Stufenplan (stage-by-stage plan) for conquest and genocide in Eastern Europe, and then the world. In the 1960s and 1970s Hillgruber was one of the leaders