Post-war, reaction to Nazi annihilation of avant-garde / Rehabilitation of Expressionism, string of exhibitions / 20th-Century German Art, London, 1938 / General Exhibition of German Art, Dresden, 1946 / Documenta I, Kassel, 1955 / German avant-garde alongside international art / Market recovery / 1961, Baron Thyssen started collecting Expressionist art / Aided by Roman Norbert Ketterer, promotor of modern art / Contribution to redeeming German artists.