Looking back, few would question the rectitude of the Allied powers' mission to stop Hitler's army as it steamrolled across Europe. Then and now, the Second World War has been presented as a moral crusade – a just war, even. As the Nazis advanced eastwards, they cleared the territory they conquered of "undesirables" through expulsion and murder. This they did to secure Lebensraum (living space) in the firm belief that more land was key to restoring Germany to its rightful place in the world.

While German aggression has been well documented, comparatively little attention has been paid to the expulsion of ethnic Germans living in Eastern Europe after the war, somewhat vindicating the saying that "history is a tale told by the victors". The Allies oversaw the largest forced population transfer in history: 12 million German-speaking civilians living in Czechoslovakia, Hungary and Poland were forced to leave their homes and made to resettle in defeated Germany. Figures vary, but between 500,000 and 1.5 million of these expellees died, of maltreatment in the holding camps before they left, of starvation on the expulsion trains, or of disease when they arrived in the Fatherland.

The Allied rationale for the forced population movements is worth considering. On the one hand, Allied leaders believed that the level of hatred towards the ethnic Germans in Eastern Europe would be so great after the war that it would be kindest to remove them, for fear of wholesale massacre. On the other, the Allies felt that it was unfair on Czechoslovakians, Hungarians and Poles to have to tolerate ethnic Germans in their midst, given the scale of suffering wrought by the Third Reich. In spite of the wording of the Potsdam Agreement, which declared that the expulsions should be carried out in an "orderly and humane" fashion, Douglas convincingly shows that the Allies had a very clear idea of the scale of suffering that implementing such a policy would bring. As early as 1942, a Foreign Office think-tank investigated the implications of a mass expulsion of ethnic Germans. The report concluded that "If the Allies did not wish to see central Europe's road and rail network congested with expellees, a timescale of five to ten years would be required." It went on to say that because it was unlikely that the expelling states would wait that long "the surviving Germans would have to be herded into concentration camps in Germany" while adequate settlement plans were organised.

These findings, it seems, were far too negative for the politicians, who were determined to pursue the policy irrespective of the human cost. The Allies knowingly pursued this course of action in the firm belief that the consequent suffering would have an educational effect on the defeated Germans. Even before the war was over, Eastern Europeans took matters into their own hands, expelling ethnic Germans from their territories. With little warning, they were forced from their homes and pointed west. Taking no more provisions than they could carry, expellees were forced to beg and steal. Even this did not ensure their survival. A number of occupation troops stationed in Germany voiced their shock at the terrible state of the refugees arriving from the East. One soldier declared that "the removal of the dead in carts from the railway stations was a grim reminder of what I saw in Belsen".

In overseeing the expulsion of ethnic Germans, the Allies soon found that they had created a humanitarian crisis in which refugees were pouring into bomb-ravaged Germany with little more than the clothes on their backs. At the end of 1947 the Allied Control Council declared "opposition to all future compulsory population transfers, particularly the forcible removal of persons from places which have been their homes for generations."

The expulsion of Germans is understandably a politically-charged topic. Until recently it has been taboo to examine the depths of German suffering after 1945, because of the suffering they themselves had caused. Drawing on meticulous research, Douglas thoughtfully explains the context for this policy, before showing convincingly that its rationale was flawed.