During the German invasion of Poland, which started World War II, Nazi Germany carried out a number of atrocities involving Polish prisoners of war (POWs). During that period, the Wehrmacht is estimated to have mass murdered at least 3,000 Polish POWs, with the largest atrocities being the Ciepielów massacre of 8 September 1939 and the Zambrów massacre of 13–14 September. Most of those atrocities are classified as war crimes of the Wehrmacht. Jewish soldiers with the Polish Army were also more likely than others to be victims of various atrocities.

The Holocaust was the genocide of European Jews during World War II. Between 1941 and 1945, Nazi Germany and its collaborators systematically murdered some six million Jews across German-occupied Europe, around two-thirds of Europe's Jewish population. The murders were carried out primarily through mass shootings and poison gas in extermination camps, chiefly Auschwitz-Birkenau, Treblinka, Belzec, Sobibor, and Chełmno in occupied Poland. Separate Nazi persecutions killed a similar or larger number of non-Jewish civilians and POWs; the term Holocaust is sometimes used to refer to the persecution of these other groups.