Adolf Hitler believed that the Polish elites might inspire the Poles to disobey their new German masters so he decreed that they had to be eliminated beforehand. The aim was the elimination of Polish society's elite, which was very broadly defined as: Polish nobles, intelligentsia, teachers, entrepreneurs, social workers, military veterans, members of national organizations, priests, judges, political activists, and anyone who had attended secondary school. It was continued by the German AB-Aktion operation in Poland in the spring and summer of 1940, which saw the massacre of Lwów professors and the execution of about 1,700 Poles in the Palmiry forest. Several thousand civilians were executed or imprisoned. The "Einsatzgruppen" were also responsible for the indiscriminate killing of Poles during the 1941 German invasion of the Soviet Union (which itself had invaded a sizeable portion of pre-WWII Polish territory, killing dozens of thousands of imprisoned Poles in turn).Our strength is our quickness and our brutality... I have given the order—and will have everyone shot who utters but one word of criticism—that the aim of this war does not consist in reaching certain geographical lines, but in the enemies’ physical elimination. Thus, for the time being only in the east, I put ready my Death’s Head units, with the order to kill without pity or mercy all men, women, and children of the Polish race or language... Adolf Hitler, Obersalzberg Speech, given on 22 August 1939, a week before the invasion