Although the majority of Ukrainians fought in or alongside the Red Army and Soviet resistance , in Western Ukraine an independent Ukrainian Insurgent Army movement arose ( UPA , 1942 ) . Created as armed forces of the underground ( Organization of Ukrainian Nationalists , OUN ) which had developed in interwar Poland as a reactionary nationalist organization . During the interwar period , the Polish government 's policies towards the Ukrainian minority were initially very accommodating , however by the late 1930s they became increasingly harsh due to civil unrest . Both organizations , OUN and UPA supported the goal of an independent Ukrainian state on the territory with a Ukrainian ethnic majority . Although this brought conflict with Nazi Germany , at times the Melnyk wing of the OUN allied with the Nazi forces . Also , UPA divisions carried out massacres of ethnic Poles , killing around 100,000 Polish civilians , which brought reprisals . After the war , the UPA continued to fight the USSR until the 1950s . At the same time , the Ukrainian Liberation Army , another nationalist movement , fought alongside the Nazis
massacres of ethnic Poles
Massacres of Poles in Volhynia and Eastern Galicia
Ukraine