Gangs in Los Angeles have a reputation for violence, criminality, and taking over whole neighborhoods. But LA gangs have a long history, some going back over a century, and while they're now criminal organizations, some began very differently. A number of gangs started simply as organizations devoted to protecting minority groups from racial violence at the hands of either the white majority or other gangs.
Many well-known Los Angeles gangs, such as the Crips, Bloods, and Mexican Mafia, are not one organization, but dozens or even hundreds of "cliques" based in different parts of the city. These cliques feud not only with other gangs, but also with other cliques in the same gang. There's very little unity among these groups - except when their members go to prison. Then they become unified, almost always by racial lines.
What gangs are in Los Angeles? This list has them all.
18th Street Gang
West Coast Bloods
38th Street Gang