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 December 27 to December 30, 1919, the twelfth national congress of the FVdG was held in Berlin.