this was the German campaign of extermination of the Polish intelligentsia and other elements thought likely to resist (e.g. Operation Tannenberg). From 1941, disease and hunger also began to reduce the population. Poles were deported in large numbers to work as forced labour in Germany: eventually about a million were deported, and many died in Germany. Treatment of Polish citizens under Soviet occupation By the end of the Polish Defensive War, the Soviet Union took over 52.1% of Poland's territory (~200,000 km2), with over 13,700,000 people. The estimates vary; Prof. Elżbieta Trela-Mazur gives the following numbers in regards to the ethnic composition of these areas: 38% Poles (ca. 5.1 million people), 37% Ukrainians, 14.5% Belarusians, 8.4% Jews, 0.9% Russians and 0.6% Germans. There were also 336,000 refugees from areas occupied by Germany, most of them Jews (198,000). Areas occupied by the USSR were annexed to Soviet territory, with the exception of the Wilno area, which was transferred to Lithuania, although it was soon attached to the USSR once Lithuania became a Soviet republic. Initially the Soviet occupation gained support among some members of the linguistic minorities who had chafed under the nationalist policies of the Second Polish Republic. Much of the Ukrainian population initially welcomed the unification with the Soviet Ukraine because twenty years earlier their attempt at self-determination failed during both the Polish–Ukrainian War and the Ukrainian–Soviet War. There were large groups of prewar Polish citizens, notably Jewish youth and, to a lesser extent, the Ukrainian peasants, who saw the Soviet power as an opportunity to start political or social activity outside their traditional ethnic or cultural groups. Their enthusiasm however faded with time as it became clear that the Soviet repressions were aimed at all groups equally, regardless of their political stance. British historian Simon Sebag Montefiore states that Soviet terror in the occupied eastern Polish lands was as cruel and tragic as the Nazis' in the west. Soviet authorities brutally treated those who might oppose their rule, deporting by 10 November 1940 around 10% of total population of Kresy, with 30% of those deported dead by 1941. They arrested and imprisoned about 500,000 Poles during 1939–1941, including former officials, officers, and natural "enemies of the people" like the clergy, but also noblemen and intellectuals. The Soviets also executed about 65,000 Poles. Soldiers of the Red Army and their officers behaved like conquerors, looting and stealing Polish treasures.