 As the left wing of the USPD merged with the Communist Party of Germany (KPD), Bästlein and his wife joined the KPD.In March 1921, Bästlein was elected to the "Hamburgische Bürgerschaft", the legislature of Hamburg.At that time, decisions urged by the Communist International, caused the KPD to incite unrest in Saxony and the Ruhr region.