In 1886, he joined the outlawed political party Sozialistische Arbeiterpartei (the precursor of the modern SPD, Sozialdemokratische Partei Deutschlands).
The following year he began his magnum opus, an examination of moral practice, Sittengeschichte, eventually running to six volumes by 1912.
While engaged in this series, he followed up his interest in caricatures with one devoted to the representation of women, Die Frau in der Karikatur, 1905 (3 vols).
Vladimir Lenin's government put him in charge of prisoner exchange with Germany after the war; he was among the leaders of the German Comintern in Berlin in 1919.
Fuchs' collection included19 paintings by Max Liebermann as wella as majolica and porcelain and East Asian objects.
Fuchs and his wife, who was Jewish, escaped Nazi Germany in February 1933 via Schaffhausen, Strasbourg and Geneva to Paris.
On 25 March 1933 a large-scale Gestapo operation took place at the Villa Fuchs, ostensibly to secure "communist evidence.
[11] A triptych by Max Slevogt, Der verlorene Sohn (The Prodigal Son), that had belonged to Fuch was restituted to his heirs by the Staatsgalerie Stuttgart which had received it as a gift from the German art collector Otto Stäbler.