the main fascist party in Germany. This was based on the theory of social fascism that had been proclaimed by Joseph Stalin and that was supported by the Comintern during the late 1920s and early 1930s, which held that social democracy was a variant of fascism. Consequently, the KPD held that it was "the only anti-fascist party" in Germany and stated that "fighting fascism means fighting the SPD just as much as it means fighting Hitler and the parties of Brüning." In KPD and Soviet usage, fascism was primarily viewed as the final stage of capitalism rather than a specific group or movement such as the Italian Fascists or the German Nazis and, based on this theory, the term was applied quite broadly. In 1929, the KPD's banned public May Day rally in Berlin was broken up by police; 33 people were killed in the clash and subsequent rioting. The RFB was then banned as extremist by the governing Social Democrats. In 1930, the KPD established the RFB's de facto successor, known as ("Fighting Alliance against Fascism"). In late 1931, local Roter Massenselbstschutz ("Red Mass Self-Defence") units were formed by Kampfbund members as autonomous and loosely organized structures under the leadership of, but outside the formal organization of the KPD as part of the party's united front policy to work with other working class groups to defeat "fascism" as interpreted by the party. During the Third Period, the KPD viewed the Nazi Party ambiguously. On one hand, the KPD considered the Nazi Party to be one of the fascist parties. On the other hand, the KPD sought to appeal to the Strasserite-wing of the Nazi movement by using nationalist slogans. The KPD sometimes cooperated with the Nazis in attacking the SPD. In 1931, the KPD had united with the Nazis, whom they referred to as "working people's comrades", in an unsuccessful attempt to bring down the SPD state government of Prussia by means of a referendum. In the usage of the Soviet Union, and of the Comintern and its affiliated parties in this period, including the KPD, the epithet fascist was used to describe capitalist society in general and virtually any anti-Soviet or anti-Stalinist activity or opinion. The formation of Antifaschistische Aktion in 1932 indicated a shift away from the Third Period policies, as fascism came to be recognised as a more serious threat (the two red flags on its