Nazi forces had begun the mass killing of Jews as early as 1939, when Germany first invaded Poland. These actions expanded greatly during the invasion of the USSR in 1941. By 1942, the so-called Endlösung, or “final solution,” took shape, as the murders become increasingly systematic and Hitler pressed his underlings to speed up the process. During the previous year, S.S. commanders had experimented with different methods, and gas chambers proved to be the method of choice.
Although prisoners died by the thousands from disease, overwork, or starvation in German labor camps throughout Europe, there were only seven designated extermination camps. Six were located in Poland, one in Belorussia. These camps existed purely for the purpose of killing, and most of the prisoners taken to them were dead within hours of arrival. A limited number of prisoners deemed fit enough to work were temporarily forced to labor in these camps, but they were underfed and overworked until they too were unfit for labor and subsequently killed.
More than 90 percent of the victims sent to these extermination camps were Jews, brought in from all over Germany and other German-controlled areas of eastern and western Europe. Romany (Gypsies) and homosexuals also lost their lives in the camps in significant numbers, as did some Soviet prisoners of war. The camps continued operation virtually unimpeded until the Allies finally liberated them near the end of the war.