 After the German Invasion of Poland Sępólno County was annexed by Nazi Germany in 1939, and it became part of Landkreis Zempelburg.During the German occupation, Poles were subject to persecutions, mass arrests, expulsions and massacres.Numerous Poles were imprisoned in a concentration camp in Radzim and in a prison established by the "Selbstschutz" in Sępólno Krajeńskie, and later murdered there or deported to other Nazi concentration camps.