The ethnic cleansing and territorial reconfiguration of postwar Poland was a vast undertaking. It involved expelling millions of Germans who remained east of the Oder-Neisse line, in spite of the mass flight of the majority of the population in the last months of the war. In their place, the Polish state sought to settle millions of former slave laborers and colonists, as well as Polish expellees from the Kresy, while sorting through another million citizens of the Third Reich who claimed to be of Polish descent. Most of this work had to be carried out while integrating over 115,000 square kilometers of devastated formerly German territory into the new Polish state and reintegrating a further 91,000 square kilometers of prewar Polish territory that had been incorporated directly into Nazi Germany for almost five years. Carrying this out in a politically divided, war-ravaged country required Poles to cooperate with each other and with international authorities. This was difficult, as the distance separating most Poles from the Soviet-imposed Communist regime that ruled over them was wide—and growing wider—in 1944 and 1945.