POWs helped German civilians escape. Hillgruber argued that the Red Army had a "fundamentally barbarous conception of war", and that the horrors perpetrated by the "Asiatic flood" of the Red Army, which he claimed were without parallel in history made the German stand in the East morally "justified". The American historian Charles S. Maier summarized Hillgruber's thesis in "Der Zusammenbruch im Osten 1944/45" as:Evoking the Wehrmacht's terrible mission in the winter of 1945, Hillgruber has written, is among the most difficult challenges a historian can face. He refers to the hallowing winter flight before the Russians. Hitler had given orders for impossible defenses of fortress cities; Soviet troops had arrived with apparent license to rape and assault. Millions of German civilians and soldiers waited for occasional trains in bombed out stations, caravanned through the Prussian forests, or precariously sailed through the Baltic to Jutland, often harassed by their own fanatic Nazi officials. Hillgruber saw the expulsion of the Germans as the culmination of a half century of horror. Hillgruber wrote:The mass expulsion of the Germans from a quarter of the territory of the 1937 Reich was a provisional end station on the journey that had begun with the spread of the idea of a rationalization of territory according to national allegiance and that had led to the nationality struggles on the European periphery during the First World War. These struggles were followed by the first genocide - that of the Armenians in Turkey - and the mass expulsions of Greeks from Asia Minor. The extermination and resettlement practices of Hitler and Stalin in their respective "spheres of influence" in the period of their partnership in 1939-41 had continued such "exchanges of populations", and mass murder had reached an extreme degree in Hitler's "Eastern War" from June 1941 onward; first the Jews in Poland and in the entire East were to be exterminated, then those in the whole of German-occupied Continental Europe. The idea of mass resettlement in East-Central Europe won ever more support - first in Great Britain and then in the United States, in a complete departure from their humanitarian traditions - as victory became more certain and as the aim of the destruction of Prussia as the allegedly permanent hard core of the German Reich became more and more clearly an actual war aim. Of the two essays in Zweierlei Untergang, one was a well-regarded summary (at least