Original sentence: Polish-Ukrainian tensions after massacres were provoked by Soviet forces, who used Poles as informants and in anti-Ukrainian punitive operations, resulting in savage reprisals
Edited sentence: It has been documented that Poles began exterminating Ukrainian civilians in some areas west of the Western Bug and San rivers in 1942.Polish-Ukrainian tensions were often provoked by Soviet forces, who used Poles as informants and in anti-Ukrainian punitive operations, resulting in savage reprisals