During the Great War, Hanns Eisler served as a front-line soldier in the Austro-Hungarian army and was wounded several times in combat. Returning to Vienna after Austria's defeat, he studied from 1919 to 1923 under Arnold Schoenberg. Eisler was the first of Schoenberg's disciples to compose in the twelve-tone or serial technique. He married Charlotte Demant in 1920; they separated in 1934. In 1925, he moved to Berlin—then a hothouse of experimentation in music, theater, film, art and politics. There he became an active supporter of the Communist Party of Germany and became involved with the November Group. In 1928, he taught at the Marxist Workers' School in Berlin and his son Georg Eisler, who would grow up to become an important painter, was born. His music became increasingly oriented towards political themes and, to Schoenberg's dismay, more "popular" in style with influences drawn from jazz and cabaret. At the same time, he drew close to Bertolt Brecht, whose own turn towards Marxism happened at about the same time. The collaboration between the two artists lasted for the rest of Brecht's life.