Realism is a form of writing that uses characters as ordinary people to endure the common course of life. This form of writing relies on biology, psychology, and sociology.
Regionalism is literature that portrays specific events in time and the feelings of the victims pursuing these instances. These forms of writing motivate people and explain realistic human conditions. (not always bad events)
Naturalism is a form of literature where the authors are always trying to change, grow, and reform society. Naturalists believe that human behavior is determined by forces beyond the individual's power-- biology and environment.