In modern usage, gang often refers to loosely organized groups that control a territory through readiness to use coordinated violence, especially against other gangs. Violence also serves to maintain organization within the gang and to control gang members Source: URL Wikipedia

Please add to this list of ways to combat gang violence.

Provide alternatives

• Attend meetings with concerned citizens to organize programs within the local school through sports, drama and activities that offer alternatives to gangs. ([http://www.ehow.com/how_2090450_stop-gang-violence.html eHow)

Work with police

• Report suspicious activity, set up a Neighborhood Watch or a community patrol; let the police know about gang graffiti, get (and share with other parents) the facts on the gang problem in your community, find out what local services - nonprofit as well as government - will work with communities against gangs. (A Better Way Out)