Why are black and mexican neighborhoods more violent then white neighborhoods?

Seriously, just admit it. Whenever I watch the news on Sunday I hear about 3-4 shooting and 4 out of 5 of the gunman are black or mexican. This only applies to big cities because I don't know what goes on in small towns. Even where I live gang graffiti has increased as the number of mexicans has increased. This didn't happen when my neighborhood was almost all white. Yeah heavy drinking and domestic violence might have been common but atleast I didn't have to live in fear of shootings.