Rudolf Rocker returned to Germany in November 1918 upon an invitation from Fritz Kater to join him in Berlin to re-build the Free Association of German Trade Unions (FVdG). The FVdG was a radical labor federation that quit the SPD in 1908 and became increasingly syndicalist and anarchist. During World War I, it had been unable to continue its activities for fear of government repression, but remained in existence as an underground organization. Rocker was opposed to the FVdG's alliance with the communists during and immediately after the November Revolution, as he rejected Marxism, especially the concept of the dictatorship of the proletariat. Soon after arriving in Germany, however, he once again became seriously ill. He started giving public speeches in March 1919, including one at a congress of munitions workers in Erfurt, where he urged them to stop producing war material. During this period the FVdG grew rapidly and the coalition with the communists soon began to crumble. Eventually all syndicalist members of the Communist Party were expelled. From 27 to 30 December 1919, the twelfth national congress of the FVdG was held in Berlin. The organization decided to become the Free Workers' Union of Germany (FAUD) under a new platform, which had been written by Rocker: the "Prinzipienerklärung des Syndikalismus" ("Declaration of Syndicalist Principles"). It rejected political parties and the dictatorship of the proletariat as bourgeois concepts. The program only recognized de-centralized, purely economic organizations. Although public ownership of land, means of production, and raw materials was advocated, nationalization and the idea of a communist state were rejected. Rocker decried nationalism as the religion of the modern state and opposed violence, championing instead direct action and the education of the workers.