The Second World War began with the invasion of Poland by the Nazi Third Reich on September 1, 1939. It was an unprovoked act of aggression by a militarily much more powerful state against its smaller neighbor. Its ultimate goal was, as indicated by Adolf Hitler, to acquire the appropriate “living space” (Lebensraum) allegedly essential for the Germans in order to boost the nation’s prosperity. According to these ideological principles, Poles living in the conquered territories in the East would have been expendable and in fact, undesirable. Not only by being unfit for Germanization because of their “racial inferiority” and virtually useless in all other respects, but also because by manifesting their hostility towards the Germans they were perceived as a potential threat. So, if in Mein Kampf Hitler barely mentions the Poles it is probably because of the conviction that discussing this issue, for obvious reasons, would have been redundant. Already in the Weimar Republic the opinion was often openly expressed, and not just among right-wing extremists, that the very existence of Poland was “unbearable” (unerträglich) to Germany.

For these reasons, the war with Poland took on an extremely brutal character. Residential houses and other buildings were burned, and Polish soldiers as well as random civilians taken prisoner were often killed. Luftwaffe pilots bombed the cities and shot at columns of refugees with machine guns. The invasion of Wehrmacht troops was also an opportunity for local Germans to settle scores with their Polish neighbors. Poles who for some reason had previously gotten into their black books or expressed their patriotism in various ways were imprisoned or murdered by German paramilitary formations such as the Volksdeutscher Selbstschutz. They were supported in these activities by special SD (Sicherheitsdienst) and security police groups (Einsatzgruppen) that operated behind the front lines right from the beginning of WWII.

The first wave of individual killings and group executions of Poles by the end of October 1939 saw the death of over 20,000 people. These crimes and persecutions did not cease after the end of hostilities or the takeover of the seized territories by the civil administration: they only assumed a more organized structure. From then on, they concerned Poles who were previously identified as "hostile" and whose names were placed on special proscription lists that were updated on a regular basis as a result of denunciations and the police agents' work.