Friedrich was actively involved in the Spartacist uprising. After the end of the war, he was a member of the youth organisation Freie sozialistische Jugend by Karl Liebknecht and Rosa Luxemburg. After its dissolution in 1920, he founded his own anarchist youth group "Freie Jugend" in Berlin. The group was also founded in Preußen, Sachsen, Thüringen, Rheinland, Westfalen as well as in Austria an Switzerland. The magazine "Freie Jugend" connected the different groups and was published by Friedrich until 1926. From 1923 on, the group fusioned with the Syndikalistisch-Anarchistische Jugend Deutschlands (SAJD), an anarcho-syndicalist youth movement that promoted antimilitarism. In between the two World Wars, he was an antimilitarist activist. Among other activities, he was a speaker at an anti-war demonstration in front of Berlin Cathedral on 31 July 1921 that had over 100,000 participants.