Naturalists, like Stephen Crane and Jack London, felt that free will was an illusion. In reality, we're all controlled by the world we live in, by nature, society, and heredity. Nature has the biggest influence, dictating illnesses, our biological instincts and emotions, and even the weather when traveling across seas and wilderness. The most we can hope for is to survive as long as possible. Naturalist writers often wrote of the darker side of society, for example, Upton Sinclair's book The Jungle, which talked of the brutal lives of immigrant workers in Chicago meat packaging factories. It led to the Meat Inspection Act of 1906. And Stephen Crane wrote about life in slums, about crime, homelessness, and prostitution.
Regionalism was a movement led by the curiosity of readers to know what was happening in different parts of America, and to learn what different places looked like, how people acted, their manners, and what regional dialect they used. Writers focused on places like Maine, Massachusetts, Georgia, Louisiana, Indiana, and California. Regionalist authors focused on slang and accents, changing the spelling of many words in dialogue.