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.