history of Poland from 1939 to 1945 encompasses primarily the period from the Invasion of Poland by Nazi Germany and the Soviet Union to the end of World War II . Following the German-Soviet non-aggression pact , Poland was invaded by Nazi Germany on 1 September 1939 and by the Soviet Union on 17 September . The campaigns ended in early October with Germany and the Soviet Union dividing and annexing the whole of Poland . After the Axis attack on the Soviet Union in the summer of 1941 , all of Poland was occupied by Germany . Under the two occupations , Polish citizens suffered enormous human and material losses . According to the Institute of National Remembrance estimates , about 5.6 million Polish citizens died as a result of the German occupation and about 150,000 died as a result of the Soviet occupation . The Jews were singled out by the Germans for a quick and total annihilation and about 90 % of Polish Jews ( close to three million people ) were murdered as part of the Holocaust . Jews , Poles , Romani people and prisoners of many other ethnicities were killed '' en masse '' at Nazi extermination camps , such as Auschwitz , Treblinka and Sobibór . Ethnic Poles were subjected to both Nazi German and Soviet persecution . The Germans killed an estimated two million ethnic Poles . They had future plans to turn the remaining majority of Poles into slave labor and annihilate those perceived as “ undesirable ” as part of the wider '' Generalplan Ost '' . Ethnic cleansing and massacres of Poles and to a lesser extent Ukrainians were perpetrated in western Ukraine ( prewar Polish Kresy ) from 1943 . The Poles were murdered by Ukrainian nationalists
massacres of Poles
Massacres of Poles in Volhynia and Eastern Galicia
History of Poland (1939–1945)