SPACE & TIME TRAVEL
Space travel is a classic science-fiction genre in which the action occurs in space, either aboard a spaceship or on another planet. Stories in the time travel subgenre involve characters traveling into the past or the future, whether it's by technology or science, looking to change something.
MILITARY SCI-FI
Military science fiction will often have a story that revolves around war or a military conflict. Of course, most of the characters will be military members and have strong themes about duty, honor, or heroism.
SCI-FI
DYSTOPIAN & ALIEN INVASION
The dystopian genre imagines worlds or societies where life is extremely bad because of deprivation or oppression or terror, with characters who battle environmental ruin, technological control, and government oppression. Alien invasion is a common theme in science fiction stories and film, in which a technologically-superior extraterrestrial society invades Earth with the intent to replace human life, or to enslave it under a colonial system, or in some cases, to use humans as food.