 Freed by the November Revolution, Kraemer returned in 1918 to Siegen, where he was active in the workers' and soldiers committee.He joined the Independent Social Democratic Party of Germany (USPD) and took part in March 1920 in the fighting in the wake of the Kapp Putsch on the side of the Ruhr Red Army, in which he served as a section commander.Towards the end of 1920 he joined the Communist Party, and was organisation secretary in the subdistrict - he scored victories and from 1923 to 1925 he represented the Communist Party in the city council.