How was the writing style used in Realism changed during 20th and 21st century?
Realist authors wrote as if they were simple observers of any situation. Refusing to interfere with the reality of life, Realists desired to show life as it was. Texts of this period contained open "conversations" about sex, poverty, and hate (to name a few). Given that the author's intent was in writing from a realistic point-of-view, the narrative voice tended to be third person omniscient. The settings in Realism depicted accurate images and representations of real places (or places which could exist realistically). The dialogue of the texts used real conversational slang and language. This period illustrated, sometimes, the destruction of the individual.
During the 20th and 21st centuries, Modernism emerged. Driven by global changes (science, technology, war, and psychology), the literature of the period illustrated life as it was, yet the texts focused upon the internal dialogue of the main characters. This type of text focuses upon why individuals do things (or do not do things) based upon how he or she looks at and interprets life. Modernist writers also used allusion (literary device). The inclusion of allusions allowed the writers to bring the past into the present and future. Unlike Realism which depicted the destruction of the individual, Modernists tended to write about the destruction of all (as seen in T. S. Eliot's "The Waste Land").