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.
Bergen-Belsen [ˈbɛʁɡn̩.bɛlsn̩], or Belsen, was a Nazi concentration camp in what is today Lower Saxony in northern Germany, southwest of the town of Bergen near Celle. Originally established as a prisoner of war camp, in 1943, parts of it became a concentration camp. Initially this was an "exchange camp", where Jewish hostages were held with the intention of exchanging them for German prisoners of war held overseas. The camp was later expanded to accommodate Jews from other concentration camps.