Alternate history (also alternative history, allohistory, althist, or AH) is a genre of speculative fiction in which one or more historical events have occurred but are resolved differently than in actual history. As conjecture based upon historical fact, alternate history stories propose What if? scenarios about crucial events in human history, and present outcomes very different from the historical record. Some alternate histories are considered a subgenre of literary fiction, science fiction, or historical fiction. Since the 1950s, as a subgenre of science fiction, alternative history stories feature the tropes of time travel between histories, the psychic awareness of the existence of an alternative universe, by the inhabitants of a given universe; and time travel that divides history into various timestreams. Source: Wikipedia (en)