I live right by Moss Side, 5 mins walk from my house. There is plenty of gang activity round here (Gooch, Doddington, Mad Dogs...) and it is in no way restrcted to black youths (or even youths). In fact one of the local gangs, some of who were jailed a few years ago for some very nasty break-in/carjacking including some nasty assaults (think machetes etc...), a few of which in my street, were white kids.
If it was related to domestic violence then it must be rife, ergo, no, it is a result of them growing up in areas where gang culture is a way of life and seen as some kind of right of passage and way to be to "respected" (albeit by fear), to belong to something and get away with things, a prime example being the reluctance of people to provide information to the police, like when Jessie James was shot near here.
Yes there are social factors, poverty, lack of education... and there seems to be a popularity in gangs from different ethnic backgrounds kicking off against each other, mainly I think as you do tend to get pockets of some ethnic minorities who tend to group together in their own mini communities.
Drugs are a major factor too, drugs are a major source of income for the gangs and the control of that kicks off a lot of rivalry over territory and income.