In Central America, one calls them maras. These groups of young people, built on the model of the gangs of Los Angeles, become frightening, sow terror in El Salvador. This is a study of a violent phenomenon imported from the United States. The gangs, las maras, made up of young people, covered in tattoo and dedicated to the traffic of weapons and drug, colonize little by little all of Central America. An Indirect effect of globalisation, it is in Los Angeles that the young latinos immigrants started both principal gangs who clash today in Central America: Mara Salvatrucha (known as MS) and M18, each have their own coded language, their rites and their tattoos and they hated one another. No ideological or religious differences explain this fight to the death whose origin, lost in the Hispanic barrios of Los Angeles, is forgotten by all. But the reasons for the displacement of the "battle field" southwards seem clearer. More than a quarter of the population of El Salvador lives today in the United States. Each week, a federal plane coming from Texas or California, brings back, to San Salvador, a hundred "deportees" chained to their seat. Illegal immigrants for the majority, arrested during a simple road control, or mareros (between 2 and 5%), sentenced in the United States and expelled once their sentence is carried out. These massive expulsions contribute to the development of the MS and M18 in Central America.