During the Soviet occupation, one of the first things they did was to eliminate any chance of resistance to their occupation. The NKVD already had a large number of Polish Army officers and enlisted in prisoner camps, and to these numbers added university professors, lawyers, police officers, priests, politicians, essentially anyone who could become the focal point of resistance or who could inspire others to resist. Some were just “capitalists” such as factory owners, but the majority was part of the social and civil fabric and could become potential sources of resistance. The NKVD at one point had approximately 500,000 Poles in prison camps in Poland. The NKVD proceeded to liquidate the most troublesome @22,000m of which 14,000 were captured military or police officers. Enlisted soldiers in many instances were shipped to Siberia to provide labor gangs. The executed were then collected and buried in several mass graves in the Katyn Forrest. These graves would remain hidden until the Germans overran the area during their invasion eastward. There are another estimated 130,000 executed by the Soviets during the occupation, on top of the Katyn incident. The Katyn incident is the most notorious. The Soviets justified in that Poland was never a country, just merely a rebellious extension of Belarus and Ukraine, so captured Polish army members were not afforded the rights of POWs and were simply criminals.

Initially the occupation was resented by Poles, but welcomed by ethnic Ukrainians and other minorities within the Polish boundaries. This ended quickly as it became clear the Soviets were not going to allow these groups any measure of self-determination, and would be suppressed like the Poles. The Soviets begain a process of de-Polandizing Poland. Disbanded the government, replaced the currency, the Soviets also engaged in widespread looting of Polish industry, shipping the machinery east, as well as plundering Polish national treasures, as well as petty looting of the populace. No public organizations were allowed to exist, the university and the school system had any elements of Polish culture stripped from them and were reorganized to be Soviet institutions. Sexual violence by Soviet troops appears to also have reached epidemic levels among Polish women, but historians have had only scattered and fragmented accounts and cannot accurately place a number, or even really give an accurate guess on the number of victims. (The Red Army would repeat this during their return to Poland as they drove West into Germany years later.) The Soviets began mass deportations in several cities, as well as deporting those arrested and convicted of anti-revolutionary activity or crimes against the Soviet Union. Roughly a million or so Poles were deported to Siberia and Kazakhstan. The land was reorganized according to Soviet guidelines and collectivized, as were all remaining industries. Basically, the Soviets were doing everything possible to annex and integrate the captured territory into the Soviet Union.

Between Nazis and Soviets - Jan Chodakiewicz

Katyn – Paul Allen

Poland's Holocaust - Tadeusz Piotrowski