This is how the composer Hanns Eisler described his impressions of the Reichenberg music festival in summer 1935. Eisler, who had fled from the Nazis in 1933, went on various work and concert tours in Europe and Russia during this time. 18,000 music-loving, working-class singers from northern Bohemia as well as Czech and German composers, musicians and intellectuals gathered in Reichenberg in Bohemia, just ten kilometres from the German border.

Eisler's Lied von der Einheitsfront [Song of the United Front] for orchestra and mass choir was performed at this music festival. The work had premiered just a few weeks before at the International Music Olympiad, where it at been performed by a choir of 3,000 working class singers in Strasbourg. Eisler had composed it and rehearsed it especially for the occasion. The solos were sung by Ernst Busch, one Germany's most important left-wing stage artists. Thousands joined in with Busch's voice and the Song of the United Front became very well known among German emigrants afterwards.

The inspiration for the marching-style choir music and orchestration came in 1934 from the director Erwin Piscator. The lyrics were written by Bertolt Brecht. The united front described in the song is the combined forces of all working people against Nazism. The Lied von der Einheitsfront was printed for the first time in 1937 in Spain during the Spanish Civil War; it was published by Ernst Busch.

Eisler, who had already gained experience of working with amateur choirs as a young composer, composed the work in a deliberately simple manner so that it could be effectively performed by untrained choir singers.