On 23 May 1939, Hitler explained to his officers that the object of the aggression was not Danzig, but the need to obtain German "Lebensraum" and details of this concept would be later formulated in the infamous "Generalplan Ost". The invasion decimated urban residential areas, civilians soon became indistinguishable from combatants, and the forthcoming German occupation (both on the annexed territories and in the General Government) was one of the most brutal episodes of World War II, resulting in between 5.47 million and 5.67 million Polish deaths (about one-sixth of the country's total population, and over 90% of its Jewish minority)—including the mass murder of 3 million Polish citizens (mainly Jews as part of the final solution) in extermination camps like Auschwitz, in concentration camps, and in numerous ad hoc massacres, where civilians were rounded up, taken to a nearby forest, machine-gunned, and then buried, whether they were dead or not. Among the 100,000 people murdered in the "Intelligenzaktion" operations in 1939–1940, approximately 61,000 were members of the Polish intelligentsia: scholars, clergy, former officers, and others, whom the Germans identified as political targets in the "Special Prosecution Book-Poland", compiled before the war began in September 1939.