The wartime Polish-Ukrainian conflict commenced with the massacres of Poles in Volhynia ( , literally : '' Volhynian slaughter '' ) , a campaign of ethnic mass murder in western Reichskommissariat Ukraine , which was the Polish Volhynian Voivodeship before the war . The entire conflict took place mainly between late March 1943 and August 1947 , extending beyond World War II . The actions , orchestrated and conducted largely by the UPA together with other Ukrainian groups and local Ukrainian peasants in three former Polish provinces ( voivodeships ) , resulted in between 50,000 and 60,000 Polish civilians killed in Volhynia alone . Other major regions of the slaughter of Poles were eastern Galicia ( 20,000 – 25,000 killed ) and southeastern Lublin province ( 4,000 – 5,000 killed ) . The peak of the massacres took place in July and August 1943 , when Dmytro Klyachkivsky , a senior UPA commander , ordered the extermination of the entire ethnically Polish population between 16 and 60 years of age . Hundreds of thousands of Poles fled the affected areas . The massacres committed by the UPA led to ethnic cleansing and retaliatory killings by Poles against local Ukrainians both east and west of the Curzon Line . Estimates of the number of Ukrainians killed in Polish reprisals vary from 10,000 to 20,000 in all areas affected by the conflict . Ukrainian historians give higher numbers for the Ukrainian losses . The reprisal killings were committed by the Home Army , Bataliony Chłopskie , and Polish self-defense units . They were restrained from mounting indiscriminate attacks by the Polish Government-in-Exile , whose goal was to retake and govern western Ukraine after the war . As a result of the fierce fighting that took place in May and June 1944 , a Polish-Ukrainian front had been established along the Huczwa River with several thousand participants on each side ; it ceased to exist only with the arrival of the Soviet Army
massacres of Poles in Volhynia
Massacres of Poles in Volhynia and Eastern Galicia
History of Poland (1939–1945)