The cholo phenomenon is longstanding and has developed new elements during the continual Mexican immigration in this century. Families who were unable to become socially mobile during the economic shifts and culture changes of the 20th century became a cholo subculture that was impoverished and culturally alienated from the surrounding cultures. The process intensified with each new generation, with youth gang members consisting of those who relied increasingly on street peers for socialization. In addition, the introduction of heroin and other drug dealing in the late 1940's and early 1950's helped change the gangs into more formal units. The Vietnam war eliminated a generation of role models while the War on Poverty and the Chicano movement briefly reduced gang violence. However, choloization and gang violence has intensified since this period and appears likely to continue for part of the population.