The document discusses the concentration camps established by Nazis during World War II. Six extermination camps were constructed in Poland, including Auschwitz-Birkenau, for the systematic killing of over six million mainly Jewish men, women and children. The camps had brutal living conditions and were used for slave labor, medical experimentation, and extermination. Some of the most notorious camps liberated in 1945 included Buchenwald, Dachau, and Belsen.