In 1914 her son Peter was killed in Flanders. The loss of Peter contributed to her socialist and pacifist political sympathies. In 1919 she worked on a commemorative woodcut dedicated to Karl Liebknecht, the revolutionary socialist murdered in 1919. Kathe believed that art should reflect the social conditions of the time and during the 1920s she produced a series of works reflecting her concern with the themes of war, poverty, working class life and the lives of ordinary women.