Star Trek is an American science-fiction franchise spanning six television series, ten feature films, hundreds of novels, computer and video games, and other fan stories. In Star Trek's fictional universe, humans developed faster-than-light space travel after barely surviving a 21st-century World War III. Later, humans united with other sentient species of the galaxy to form the United Federation of Planets. As a result of alien intervention and science, humanity has largely overcome many Earth-bound frailties and vices by the 23rd century. Star Trek stories usually depict the adventures of humans and aliens who serve in the Federation Starfleet.