By the fall of 1943 the OUN-B forces had established their control over substantial portions of rural areas in Volhynia and southwestern Polesia . While the Germans controlled the large towns and major roads , such a large area east of Rivne had come under the control of the OUN-B that it was able to set about creating a " state " system with military training schools , hospitals and a school system , involving tens of thousands of personnel . Its military , the UPA , which came under the command of Roman Shukhevich in August 1943 , would fight against the Germans and later the Soviets until the mid-1950s . It would also play a major role in the genocide of the Polish population from western Ukraine . For more information about the UPA , see : Ukrainian Insurgent Army
genocide of the Polish population
Massacres of Poles in Volhynia and Eastern Galicia
Organization of Ukrainian Nationalists