Clement Greenberg on Abstract Expressionism and Pop Art

Greenberg defined Modernism and believed that true 'pure' Modern art was best served by abstraction, or non-representational painting, and through his analysis of the cultural roots of "all over painting" as a reaction to industrialized society, and he became an apostle of the works of Pollock, Willem de Kooning, Robert Motherwell, David Smith, Barnett Newman, Adolph Gottlieb, Helen Frankenthaler, Franz Kline and others.
By the late 1960's Greenberg had become dissatisfied with much of abstract expressionism. He thought the works of Kline and Pollock had suffered. And after a stock crash in 1962 Greenberg believed abstract expressionist art would all but go away, soon giving rise to it's successor, Pop Art, in thanks to "middlebrow-ism."