considerable part of society held for the new regime and by disputes over Poland's postwar borders, which were not firmly established until mid-1945. The Soviet forces present at that time engaged in plunder of the former eastern territories of Germany which were being transferred to Poland, stripping them of valuable industrial equipment, infrastructure and factories and sending them to the Soviet Union. After the Soviet annexation of the Kresy territories east of the Curzon Line, about 2 million Poles were moved, transferred or expelled from these areas into the new western and northern territories east of the Oder–Neisse line, which were transferred from Germany to Poland under the Potsdam Agreement. Others stayed in what had become the Soviet Union and more went to Poland after 1956. Additional settlement with people from central parts of Poland brought the number of Poles in what the government called the Recovered Territories up to 5 million by 1950. Most of the former German population of 10 million had fled or was expelled to post-war Germany by 1950: about 4.4 million fled in the final stages of the war and 3.5 million were removed by the Polish authorities in 1945–1949. The expulsion of the Germans was the result of the Allied decisions finalized in Potsdam. With the expulsion of Ukrainians and Belarusians from Poland to the Soviet Union and the 1947 Operation Vistula dispersing the remaining Ukrainians in Poland, and with most of the Polish Jews exterminated by Nazi Germany during the Holocaust and many of the survivors emigrating to the West and to newly created Israel, Poland for the first time became an ethnically homogeneous nation state. The government-imposed and spontaneous movements of people amounted to one of the greatest demographic upheavals in European history. Unlike other European countries, Poland continued the extensive prosecution of both Nazi perpetrators and their collaborators into the 1950s. According to Alexander Prusin, Poland was the most consistent in investigating and prosecuting war crimes among the post-war communist nations; between 1944 and 1985 Polish courts tried over 20,000 defendants including 5,450 German nationals. Rebuilding of infrastructure and economy Poland suffered catastrophic damage to its infrastructure during the war, which caused it to lag even further behind the West in its industrial output. The losses in national resources and infrastructure amounted to over 30% of the pre-war potential. Poland's capital of Warsaw was among the most devastated cities – over