Flag of the Ukrainian Insurgent Army

The flag of the Ukrainian Insurgent Army (Ukrainian: Прапор УПА, romanized: Prapor UPA), also known as the red-and-black flag (Ukrainian: Червоно-чорний прапор, romanized: Chervono-chornyi prapor) or Ukrainian nationalist flag, is a flag previously used by the Ukrainian Insurgent Army (UPA) and the Bandera wing of the Organization of Ukrainian Nationalists (OUN), and now used by various Ukrainian nationalist organizations and parties, including UNA-UNSO, Right Sector, Congress of Ukrainian Nationalists and others. In Poland, the flag is widely associated with the massacres of Poles in Volhynia and Eastern Galicia.

Source: Wikipedia — Flag of the Ukrainian Insurgent Army (CC BY-SA 4.0)