'' p. '' The Polish Sanation authorities were provoked by the independence-seeking Organization of Ukrainian Nationalists ( OUN ) . OUN engaged in political assassinations , terror and sabotage , to which the Polish state responded with a repressive campaign in the 1930s , as Józef Piłsudski and his successors imposed collective responsibility on the villagers in the affected areas . After the disturbances of 1933 and 1934 , the Bereza Kartuska prison camp was established ; it became notorious for its brutal regime . The government brought Polish settlers and administrators to parts of Volhynia with a centuries-old tradition of Ukrainian peasant rising against Polish land owners ( and to Eastern Galicia ) . In the late 1930s , after Piłsudski 's death , military persecution intensified and a policy of " national assimilation " was aggressively pursued . Military raids , public beatings , property confiscations and the closing and destruction of Orthodox churches aroused lasting enmity in Galicia and antagonized Ukrainian society in Volhynia at the worst possible moment , according to Timothy D. Snyder . However , he also notes that " Ukrainian terrorism and Polish reprisals touched only part of the population , leaving vast regions unaffected " and " the OUN 's nationalist prescription , a Ukrainian state for ethnic Ukrainians alone was far from popular " . Halik Kochanski wrote of the legacy of bitterness between the Ukrainians and Poles that soon exploded in the context of World War II . See also : History of the Ukrainian minority in Poland
soon exploded
Massacres of Poles in Volhynia and Eastern Galicia
History of Poland