The document discusses factors that led to changes in 20th century novels, including: 1) The First World War, which had major political and social impacts. 2) Advances in science that changed intellectual life and reduced spirituality. 3) Growing doubts about religion as it failed to address problems. 4) Increased industrialization and the problems it brought to society. 5) Increased democracy and questioning of established authorities. Examples of famous 20th century writers and some of their important works are also mentioned.