ethnic groups, inciting and encouraging violence against Poles calling the minorities to "rectify the wrongs they had suffered during twenty years of Polish rule". Pre-war Poland was portrayed as a capitalist state based on exploitation of the working people and ethnic minorities. Soviet propaganda claimed that unfair treatment of non-Poles by the Second Polish Republic was a justification of its dismemberment. Soviet officials openly incited mobs to perform killings and robberies The death toll of the initial Soviet-inspired terror campaign remains unknown. Restoration of Soviet control While formal Polish sovereignty was almost immediately restored when the forces of Nazi Germany were expelled in 1945, however, it was quickly replaced by a self- proclaimed Polish Committee of National Liberation at the orders of Stalin. The country remained under firm Soviet control as troops of the Soviet Army Northern Group of Forces were stationed out there up until 1956. To this day the events of those and the following years are one of the stumbling blocks in Polish-Russian foreign relations. Casualties Around 6 million Polish citizens – nearly 21.4% of the pre-war population of the Second Polish Republic — died between 1939 and 1945. Over 90% of the death toll involved non-military losses, as most civilians were targets of various deliberate actions by the Germans and Soviets. Both occupiers wanted not only to gain Polish territory, but also to destroy Polish culture and the Polish nation as a whole. Tadeusz Piotrowski, Professor of Sociology at the University of New Hampshire has provided a reassessment of Poland's losses in World War II. Polish war dead include 5,150,000 victims of Nazi crimes against ethnic Poles and the Holocaust, the treatment of Polish citizens by occupiers included 350,000 deaths during the Soviet occupation in 1940–41 and about 100,000 Poles killed in 1943–44 in the Ukraine. Of the 100,000 Poles killed in the Ukraine, 80,000 perished during the massacres of Poles in Volhynia and Eastern Galicia by the Ukrainian Insurgent Army. Losses by ethnic group were 3,100,000 Jews; 2,000,000 ethnic Poles; 500,000 Ukrainians and Belarusians. In August 2009 the Polish Institute of National Remembrance (IPN) researchers estimated Poland's dead (including Polish Jews) at between 5.47 and 5.67 million (due to German actions) and 150,000 (due to Soviet), or around 5.62 and 5.82 million total. The official Polish government report prepared in 1947 listed 6,028,000 war deaths out of a population of 27,007,000 ethnic Poles and Jews;