A rule of terror was started by the NKVD and other Soviet agencies . The first victims were the approximately 230,000 Polish prisoners of war . The Soviet Union had not signed any international convention on rules of war and they were denied the status of prisoners of war . When the Soviets conducted recruitment activities among the Polish military , an overwhelming majority of the captured officers refused to cooperate ; they were considered enemies of the Soviet Union and a decision was made by the Soviet Politburo ( 5 March 1940 ) to secretly execute them ( 22,000 officers and others ) . The officers and a large number of ordinary soldiers were then murdered ( see Katyn massacre ) or sent to Gulag . Of the 10,000 – 12,000 Poles sent to Kolyma in 1940 – 41 , mostly POWs , only 583 men survived , released in 1941 – 42 to join the Polish Armed Forces in the East
Katyn massacre
Katyn massacre
History of Poland (1939–1945)