"Some groups continued to resist, especially in Ukraine and the Baltic states. Ukraine, which had been part of the Russian Empire and was taken over by Communist forces after the 1917 revolution, had come under German control in 1941, and Ukrainian nationalists used the opportunity to declare independence from the Soviet Union. While Ukrainian autonomy remained a sham under German occupation, many Ukrainian nationalists continued to fight against the Red Army after the Nazi withdrawal. The Organization of Ukrainian Nationalists (OUN) existed in the Soviet Union until 1950, when its leader, Roman Shukhevych, was killed. While the OUN was feared for its collaboration with the Nazis and its atrocities against Poles and Jews, some Ukrainians still regarded it as the champion of independence and sovereignty. Soviet countermeasures were brutal. Between 1944 and 1952 as many as six hundred thousand people were arrested in western Ukraine; about a third of these were executed and the rest imprisoned or exiled. The fierce Soviet response probably did as much to keep resistance alive as the waning military power of the OUN."