How did Marxism, Communism and Fascism impact literature of the 20th Century?

It would require completing detailed research, formulating
a thesis, and then writing a book or dissertation to really answer this question, but
some general observations and specific examples come to mind. Political philosophies,
when they are implemented in society, are always reflected and often examined in the
literature of the period. For fiction writers, political movements often become elements
of plot or are addressed thematically through their impact upon the writers' characters.
Through these methods, writers either embrace or reject the political philosophies of
their day.

Twentieth-Century literature is a very
comprehensive category, but consider American literature in the 20th Century, and it
becomes clear that Marxism, Communism, and Fascism did influence the thinking and
writing of some major authors of the time. In various novels, these political
philosophies were addressed, for instance, by John Dos Passos, John Steinbeck, and
Ernest Hemingway.

In his trilogy,
U.S.A., Dos Passos attacked the philosophy and practice of
capitalism, presenting it as an immoral political force that destroyed individual lives
and corrupted the country. When The Grapes of Wrath was published,
John Steinbeck was accused of being a communist for his condemnation of the capitalist
financial system, particularly the banking system, that he depicts as having created the
Great Depression, destroyed American lives, and then profited from their misery. His
novel, Of Mice and Men, also made a strong political statement in
showing the lives of dispossessed Americans, those without a home who live on the
fringes of American society, shut out from ever achieving the American Dream. Finally,
in Hemingway's novel, For Whom the Bell Tolls, his protagonist,
Robert Jordan, joins forces with a small band of Spanish Loyalists fighting the
fascists; Jordan chooses to die to save the others, having developed a strong sense of
community and brotherhood.

In terms of 20th-Century English
literature, Orwell's 1984 presents a chilling vision of facism in
the extreme imposed upon citizens.