faculties, also grew in strength. An ecclesiastical treaty with the Protestant regional churches in Prussia did not come about until 1931. On the state's side, it was promoted by Adolf Grimme (SPD), who had become Minister of Culture. A "political clause" that regulated the state's objections to the filling of high church positions, similar to the concordat with the Catholic Church, met with resistance from the church. Prussia and the crisis of the Republic Blood May 1929 Using sometimes drastic measures, the Prussian government tried to oppose the increasing radicalization from both the left and the right. In December 1928, following political clashes between Communists, National Socialists and Social Democrats in Berlin, the city's police chief Karl Zörgiebel issued a ban on all open-air demonstrations and gatherings. The ban applied to 1 May 1929, International Workers' Day. The KPD ignored the ban and called for a mass demonstration. Fighting resembling a civil war broke out between police and Communist supporters. Zörgiebel had ordered a crackdown and, with the SPD's approval, was determined to set an example. The fighting – which came to be known as "Blood May" – cost 33 lives, and nearly 200 people were injured. More than 1,200 arrests were made. The assumption that the KPD had planned a violent overthrow of the government could not be proven. Only later did telegrams intercepted from Moscow seem to suggest this. The Prussian government pressed for a ban of the KPD and all its subsidiary organizations. Carl Severing, who at the time was Reich Minister of the Interior, rejected the idea as unwise and impracticable. Prussia then banned the Alliance of Red Front Fighters (). With the exception of Brunswick, the other German states did the same. The events led to increased hostility in the KPD towards the Social Democrats. Ernst Thälmann, leader of the KPD, called the "social fascism" of the SPD a particularly dangerous form of fascism. He urged the KPD to direct its policies against the SPD as the "main enemy". Bulwark of democracy Even after the formation of Heinrich Brüning's (Centre Party) Reich government on 31 March 1930 and the Reichstag election of 14 September 1930, which marked the NSDAP's parliamentary breakthrough, Prussia's government continued to work for democracy and the Republic. The ban on uniforms for the NSDAP was not lifted, nor was the provision that civil servants could not belong to the anti-constitutional KPD