Alternate history

Alternate history or alternative history, sometimes abbreviated as AH, is a genre of fiction consisting of stories in which one or more historical events occur differently from reality. These stories usually contain "what if" scenarios at crucial points in history and present an outcome of events alternative to historical record. The stories are the product of conjecture, but are sometimes based on scientific fact. Alternate history can be seen as a sub-genre of literary fiction, science fiction, and/or historical fiction; different alternate history works may use tropes from any or all of these genres. Another term occasionally used for the genre is "allohistory" (literally "other history").

Since the 1950s, this type of fiction has, to a large extent, merged with science fiction tropes involving time travel between alternate histories, psychic awareness of the existence of one universe by the people in another, or time travel that results in history splitting into two or more timelines. Cross-time, time-splitting, and alternate history themes have become so closely interwoven that it is impossible to discuss them fully apart from one another.