 Complete the following phrase:   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 FVdGs alliance with the communists during and immediately after the 