On 1 May 1929 in Berlin violent street battles erupt between the police and members of the Communist Party of Germany (KPD), in particular the Red Combatants’ League (RFB).
Berlin’s police superintendent immediately declares a state of emergency in the workers’ districts of Wedding and Neukölln.
13,000 policemen are deployed brandishing firearms. After three days of unrest the toll amounts to 33 dead and over 200 injured.
This incident, remembered in the German language as Blutmai (“Blood May”), caused the SPD-lead Prussian government to outlaw the RFB a short time later.
The clashes deepened the split between the SPD and the Communist Party, which indirectly helped the German right wing parties and the eventual rise of the Nazi Party in the German parliament.
Historical Cartoon Triology on Berlin in those days: http://radicalnotes.com/content/view/109/39/