Deputy Prime Minister Piotr Gliński reminded in his letter that on July 11 and 12 Ukrainian nationalist units had carried out a massive attack on the residents of over 100 towns in the Kowel, Horochowa, Vladimir-Volynsky and Lutsky counties. Historians indicate that as a result of the Volynia Massacre in Volhynia, Eastern Galicia and Lesser Poland approximately 100-130 thousand Poles were murdered.
National Day of Remembrance of Victims of Genocide Committed by Ukrainian Nationalists against the Citizens of the Second Polish Republic was established as a holiday by the Polish Parliament in 2016. The perpetrators of the Volhynia massacre were the Organisation of Ukrainian Nationalists - a faction of Stepan Bandera, the Ukrainian Insurgent Army (UPA) subordinated to it, and the Ukrainian population participating in the murder of their Polish neighbours. UPA's action was the culmination of the wave of murdering and driving Poles out of their homes that had been going on since the beginning of 1943. Altogether in the years 1943-1945 in Volhynia and Eastern Galicia about 100 thousand Poles were killed.
Source: Poland Daily, gov.pl