What makes A Streetcar Named Desire a Modernist play?

Tennessee Williams's "A Streetcar Named Desire" is certainly modernist in its themes of alienation and ambivalence, as well as its conflict between the Old South represented by Blanche and the uncivilized, Darwinian character, Stanley Polowski.

In a criticism entitled, "Tennessee v. John T. Scopes" by John S. Bak, the author sees the play as a reechoing of the famous trial.  In "A Streetcar Named Desire," the main conflict is identified as the modernist, secular conflict with traditional, fundamentalist thinking.  The Old South, Blanche, comes into conflict with Stanley, the New South that has intruded from the industrial North. (His Polish--the Polish traditionally were blue-collar workers in factories and steel mills.)  Furthermore, in his essay, Baks likens Stanley's "tearing down of the columns" of Belle Reve, an act that Stanley tells his wife, "you loved," to the conquering of Darwin's "apes" over the Fundamentalist, religious foundation of the culture of the Old South. 

In Williams's play, Blanche DuBois arrives and, after staying a while, she decorates the house to make it more "dainty."  But, Stanley rips down the paper lantern over the bare light bulb, as well as stripping Blanche of her facade of gentility, assaulting her in the end of their argument with raw sexuality. Thus, there is a rejection in "A Streetcar Named Desire" of the moral precepts of the past as well as the aesthetics.

Like other Modernists, Tennessee Williams also emphasizes the psychological state of character through interior monologue and stream of consciousness.  Blanche DuBois is a neurotic, psychologically deluded character who vacillates between reality and the one she creates in her mind.  With this vacillating character of Blanche, also, Tennessee Williams himself comments upon the conflict between Victorian thinking and that of the moderns,

When I think of her, Blanche seems like the youth of our hearts which has to be put away for worldly considerations: poetry, music, the early soft feelings that we can't afford to live with under the naked light bulb which is now.