Both conflicts took place roughly on the same territory: The lands that are now part of western Ukraine and eastern Poland, which were claimed by Ukrainians, the ethnic majority, and the Poles who pointed to their investments into the development of these lands.
The war took place within the framework of the global conflict, World War II. The Third Reich and the USSR played a significant role in fueling the confrontation between the Ukrainians and the Poles. In the end, the border issue was solved after World War II without the participation of either, after which the Communists in the USSR and Poland changed the ethic configuration of these territories by force.
The main participants of the war were not states but underground military formations – the Ukrainian Insurgent Army (UPA) and the Polish Home Army (AK). During this war, both the militants of the UPA and AK committed war crimes, which, undoubtedly, have to be condemned. They cannot be justified as retaliations or preventive strikes.