Beginning in late 1941, the Germans began mass transports from the ghettoes in Poland to the concentration camps, starting with those people viewed as the least useful: the sick, old and weak and the very young. The first mass gassings began at the camp of Belzec, near Lublin, on March 17, 1942. Five more mass killing centers were built at camps in occupied Poland, including Chelmno, Sobibor, Treblinka, Majdanek and the largest of all, Auschwitz-Birkenau. From 1942 to 1945, Jews were deported to the camps from all over Europe, including German-controlled territory as well as those countries allied with Germany. The heaviest deportations took place during the summer and fall of 1942, when more than 300,000 people were deported from the Warsaw ghetto alone.
Though the Nazis tried to keep operation of camps secret, the scale of the killing made this virtually impossible. Eyewitnesses brought reports of Nazi atrocities in Poland to the Allied governments, who were harshly criticized after the war for their failure to respond, or to publicize news of the mass slaughter. This lack of action was likely mostly due to the Allied focus on winning the war at hand, but was also a result of the general incomprehension with which news of the Holocaust was met and the denial and disbelief that such atrocities could be occurring on such a scale. At Auschwitz alone, more than 2 million people were murdered in a process resembling a large-scale industrial operation. A large population of Jewish and non-Jewish inmates worked in the labor camp there; though only Jews were gassed, thousands of others died of starvation or disease. During the summer of 1944, even as the events of D-Day (June 6, 1944) and a Soviet offensive the same month spelled the beginning of the end for Germany in the war, a large proportion of Hungary’s Jewish population was deported to Auschwitz, and as many as 12,000 Jews were killed every day.