UPA and OUN

The Organisation of Ukrainian Nationalists was founded in Vienna in 1929 and sought an independent Ukrainian state, in the interwar years also through assassinations in Poland. In 1940 it split into the factions of Stepan Bandera (OUN-B) and Andriy Melnyk (OUN-M). From 1942 the OUN-B built up the Ukrainian Insurgent Army, commanded from 1943 by Roman Shukhevych. The UPA fought the Germans, the Soviet partisans and the Polish underground, and after the war the Soviet and Polish authorities.

In 1943 the OUN-B and the UPA began a campaign to remove the Polish population, first in Volhynia and then in Eastern Galicia, which culminated in Bloody Sunday on 11 July 1943. According to estimates by Poland's Institute of National Remembrance (IPN), 80,000 to 120,000 Poles were killed; the IPN classifies these crimes as genocide. Ukrainians who helped Poles were also among the victims. How to judge the UPA remains one of the most difficult issues in Polish–Ukrainian relations. Its activity in Poland was effectively ended by Operation Vistula in 1947.