Erich Fromm, once a member of the Frankfurt School, left the group at the end of the 1930s. The culmination of Fromm's social and political philosophy was his book "The Sane Society", published in 1955, which argued in favor of humanist, democratic socialism. Building primarily upon the works of Marx, Fromm sought to re-emphasise the ideal of personal freedom, missing from most Soviet Marxism, and more frequently found in the writings of classic liberals. Fromm's brand of socialism rejected both Western capitalism and Soviet communism, which he saw as dehumanizing and bureaucratic social structures that resulted in a virtually universal modern phenomenon of alienation.