What are the characteristics of 20th century literature in Animal Farm?

First and foremost, Orwell uses the work to comment on the rise of totalitarian systems of government in Europe in the first half of the twentieth century. The Stalinist Soviet Union is principally what he is describing, but he also has the fascist governments of Hitler and Mussolini in mind. He is trying to show the way a small group can get a total hold on power in a country and use it to oppress most of the people. Clearly, this was a deep concern in the twentieth century, as such complete tyrannies led to wars and human rights abuses.
Second, Animal Farm represents a certain stream of twentieth century writing that is simple, short, and stark, unlike the huge and embellished Victorian novels of an earlier period. Literacy had become almost universal in the developed countries in the twentieth century, and Orwell was writing for a mass audience. He was not making references to, say, Greek and Roman authors (except for Snowball studying the campaigns of Julius Caesar), because he knew his audience was probably not schooled in the classics.