Do you want to have a disturbing experience? Then read the book "This Is for the Mara Salvatrucha: Inside the MS-13, America's Most Violent Gang" by Samuel Logan (Hyperion, 2009). The word "mara" is Spanish for "gang," and the word Salvatrucha in El Salvador is slang for "street smart."
This juvenile gang was formed in 1980s Los Angeles by immigrants who were fleeing the civil war in El Salvador. But since many of the founders were former guerrilla fighters, they brought with them a cavalier attitude toward life and death. This in turn facilitated their use of extreme violence that even shocked other gangs in the area. But it also enabled MS-13 eventually to take control of large amounts of gang territory.
By 1996, the U.S. government adopted a policy of deporting MS-13 members back to their countries of origin, in many cases after serving jail or prison sentences here. Unfortunately in many ways that strategy backfired, because it resulted in the deportees using their knowledge, experiences and prison connections to form similar MS-13 gangs around the world.