Fantasy focuses on characters, creatures and events that are not explainable by known science. There is often a strong element of adventure or romance. Historical Fiction Benchmark authors could be Bernard Cornwell, Judith Tarr or Jean Auel. The rule of thumb for historical fiction is that events take place at least one generation ago, therefore, fiction set during the Vietnam War is considered historical. Includes adventure fiction in other times, such as Patrick O'Brian, W. E. B. Griffin and Philip McCutchan.
Horror fiction is essentially very dark fantasy written with the intent to frighten the reader.
Generally, supernatural or occult elements distinguish horror from thrillers, where a serial killer may be frightening, but is all too human. These books will be primarily Christian fiction, although the Zion Covenant series by the Thoenes is a good example of Jewish inspirational fiction. Stories often focus on a crisis of faith, or a difficult decision that is guided by faith. Setting is often historical, so these titles may be included in Historical Fiction as well. The benchmark authors are of course, John Grisham and Scott Turow.