Poland's territory was divided between Nazi Germany and the USSR, and was governed directly by the occupying countries, without establishing any form of Polish collaborating puppet authorities.

Wehrmacht (the German armed forces) was sent out without a formal declaration of war "to kill without mercy and reprieve all men, women and children of the Polish race", as ordered by Adolf Hitler in his speech to military commanders on 22 August 1939.

[c] On 4 September 1939 the 42nd Infantry Regiment committed the Częstochowa massacre with 1,140 citizens or more, 150 of them Jews, murdered in wild shooting actions in several city locations, leading to a final bloodbath according to Polish reports, involving frightened and inexperienced troops opening machine gun fire at a crowd of 10,000 civilians rounded up as hostages in the Main Square.

[39] The German army did not consider captured servicemen to be combatants because they fought differently from them, often avoiding direct confrontation in favor of guerrilla tactics in the face of overwhelming force.

[48] Amongst the Polish cities and towns bombed at the beginning of war were Brodnica, Bydgoszcz, Chełm, Ciechanów, Kraków, Częstochowa, Grodno, Grudziądz, Gdynia, Janów, Jasło, Katowice, Kielce, Kowel, Kutno, Lublin, Lwów, Olkusz, Piotrków, Płock, Płońsk, Poznań, Puck, Radom, Radomsko, Sulejów, Warsaw, Wieluń, Wilno, and Zamość.

Immediately after invasion, the Germans employed the earlier prepared Special Prosecution Book-Poland to launch the Operation Tannenberg campaign of mass murders and concentration camps incarcerations.

Other execution sites included Rawicz, Grodzisk Wielkopolski, Nowy Tomyśl, Międzychód, Żnin, Września, Chełmno, Chojnice, Kalisz and Włocławek.

[65] The German occupiers subsequently launched AB-Aktion in May 1940—a further plan to eliminate the Polish intelligentsia and leadership class,[66] culminating in the Palmiry massacre (December 1940 – July 1941), in which two thousand Poles perished.

[73] The large-scale pacification operations, sometimes called "anti-partisan actions", constituted the core policy of the Nazi regime against Poland and resulted in the death of approximately 20,000 people in less than two years following the invasion.

[78] The most severe of them took place in the Wola district,[79] where at the beginning of August 1944 tens of thousands of civilians (men, women, and children)[80] were methodically rounded-up and executed by Einsatzkommandos of Sicherheitspolizei operating within the Reinefarth's group of forces under the command of Erich von dem Bach-Zalewski.

Some 400 patients, along with medical staff,[97] were transported to a military fortress in Poznań where, in Fort VII bunkers, they were gassed with carbon monoxide delivered in metal tanks.

[98] As part of the concerted effort to destroy Polish cultural heritage, the Germans closed universities, schools, museums, public libraries, and dismantled scientific laboratories.

[12] The Gentile population of Polish metropolitan cities was targeted for enslavement in the łapanka actions, in which the detachments of SS, Wehrmacht and police rounded up civilians after cordoning off streets.

While the treatment of factory workers or farm hands often varied depending on the individual employer, Polish labourers as a rule were compelled to work longer hours for lower wages than Western Europeans,[113] and in many cities, they were forced to live in segregated barracks behind barbed wire.

[115] The camp system where Poles were detained, imprisoned and forced to labour, was one of fundamental structures of the Nazi regime, and with the invasion of Poland became the backbone of German war economy and the state organized terror.

[116] The incomplete list of camp locations with at least one hundred slave labourers, included in alphabetical order: Andrychy, Antoniew-Sikawa, Augustów, Będzin, Białośliwie, Bielsk Podlaski, Bliżyn, Bobrek, Bogumiłów, Boże Dary, Brusy, Burzenin, Chorzów, Dyle, Gidle, Grajewo, Herbertów, Inowrocław, Janów Lubelski, Kacprowice, Katowice, Kazimierza Wielka, Kazimierz Dolny, Klimontów, Koronowo, Kraków-Podgórze, Kraków-Płaszów, Krychów, Lipusz, łysaków, Miechowice, Mikuszowice, Mircze, Mysłowice, Ornontowice, Nowe, Nowy Sącz, Potulice, Rachanie, Słupia, Sokółka, Starachowice, Swiętochłowice, Tarnogród, Wiśnicz Nowy, Wierzchowiska, Włoszczowa, Wola Gozdowska, Żarki, and Zarudzie.

The new killing method originated from the earlier practise of gassing thousands of unsuspecting hospital patients at Hadamar, Sonnenstein and other euthanasia centres in the Third Reich, known as Action T4.

[150] In Chełmno extermination camp, the SS Totenkopfverbände used mobile gas vans to murder mostly Polish Jews imprisoned at the Łódź Ghetto (Litzmannstadt in German).

At least 152,000 people were gassed at Chełmno according to postwar verdict by West Germany,[151] although up to 340,000 victims were estimated by the Polish Main Commission for Investigation of German Crimes in Poland (GKBZNwP), a predecessor of the Institute of National Remembrance.

[156][157] The Polish scholar Franciszek Piper, the chief historian of Auschwitz, estimates that 140,000 to 150,000 Poles were brought to that camp between 1940 and 1945, and that 70,000 to 75,000 died there as victims of executions, of medical experiments, and of starvation and disease.

[165] With many Jews already executed or fleeing, the organized groups of Ukrainian nationalists under Mykola Lebed began to target ethnic Poles,[5] including pregnant women and children.

Nazi Germany also committed crimes against citizens of other countries deported to occupied Poland, especially Soviet and Italian prisoners of war, who were deliberately neglected and starved, deprived of rudimentary sanitation and medical care, resulting in numerous epidemics, or executed.

[192] Polish regular troops in Lviv, including police forces, voluntarily laid down their arms after agreeing to the Soviet terms for surrender, which offered them the freedom to travel to neutral Romania and Hungary.

[194] Following the invasion, in April and May 1940 the NKVD secret police perpetrated the single most notorious wartime atrocity against any prisoners of war held by the Soviet Union.

[195][200][199] Among the victims of the massacre were 14 Polish generals, including Leon Billewicz, Bronisław Bohatyrewicz, Xawery Czernicki (admiral), Stanisław Haller, Aleksander Kowalewski, Henryk Minkiewicz, Kazimierz Orlik-Łukoski, Konstanty Plisowski, Rudolf Prich (murdered in Lviv), Franciszek Sikorski, Leonard Skierski, Piotr Skuratowicz, Mieczysław Smorawiński and Alojzy Wir-Konas (promoted posthumously).

[201] An estimated 1.2 to 1.7 million Polish nationals (entire families with children, women, men, and elderly) were loaded onto freight trains and deported to the eastern parts of the USSR, the Urals, and Siberia.

Monuments were destroyed (for example, in Wołczyn, the remains of King Stanisław August Poniatowski were ditched), street names changed, bookshops closed, libraries burned and publishers shut down.

[223] The Soviets left thousands of corpses piled up in prison yards, corridors, cells, basements, and NKVD torture chambers, as discovered by the advancing Germans in June–July 1941.

The locations in alphabetical order included: Augustów prison: (with 30 bodies); Berezwecz: (with 2000, up to 3000 dead); Białystok: (with hundreds of victims); Boryslaw, (dozens); Bóbrka: (9–16); Brzeżany: (over 220); Busk: (about 40); Bystrzyca Nadwornianska, Cherven, Ciechanowiec: (around 10); Czerlany: (180 POWs); Czortków, Dobromil: (400 murdered); Drohobycz: (up to 1000); Dubno: (around 525); Grodno: (under 100); Gródek Jagiellonski: (3); Horodenka, Jaworów: (32); Kałusz, Kamionka Strumilowa: (about 20); Kołomyja, Komarno, Krzemieniec: (up to 1500); Lida, Lwów (over 12,000 murdered in 3 separate prisons); Łopatyn: (12); Łuck: (up to 4000 bodies); Mikolajów, Minsk: (over 700); Nadworna: (about 80); Oleszyce, Oszmiana: (at least 60); Otynia: (300); Pasieczna, Pińsk: ("dozens to hundreds"); Przemyślany: (up to 1000); Równe: (up to 500); Rudki: (200); Sambor: (at least 200, up to 720); Sarny: (around 90); Sądowa Wisznia: (about 70); Sieniatycze: (15); Skniłów: (200 POWs); Słonim, Stanisławów: (about 2800); Stryj: (at least 100); Szczerzec: (about 30); Tarasowski Las: (about 100); Tarnopol: (up to 1000); Wilejka: (over 700); Wilno: (hundreds); Włodzimierz Wołynski, Wołkowysk: (seven); Wołożyn: (about 100); Wolozynek, Zalesiany, Zaleszczyki, Zborów: (around 8); Złoczów: (up to 750); Zółkiew: (up to 60) and Zydaczów.

[235] After several months of brutal interrogation and torture,[236] 16 leaders of the Polish Underground State were sent to jails in the USSR after a staged trial on trumped-up charges in Moscow.