Complex sentence: After Soviet partisans became hostile towards Polish units loyal to the Polish government in exile, and have dealt several blows to the Poles, arresting most of the local Polish commanders, in December 1943 Pilch reorganized the Polish partisans in the Nowogródek area.
Split into simpler sentences: After Soviet partisans became hostile towards Polish units loyal to the Polish government in exile, the Soviets dealt several blows to the Poles, arresting most of the local Polish commanders. In December 1943 Pilch reorganized the Polish partisans in the Nowogródek area.