This is basically primate studies in an urban setting. The behavior of gang members is very similar to what is seen in tribes of chimps and baboons when senior males are absent: highly dysfunctional behavior by less mature males, centered around temporary alliances and high levels of violence. Stabilization only occurs when either (i) mature males are introduced artificially, or (ii) a tiny percentage of immature males survive to full adulthood and begin to exercise a slight stabilizing influence. As these males, however, will have matured during great dysfunction, stabilization may take many generations to complete. The outlook for US city gangs is therefore fairly dismal unless social engineering is undertaken on a large scale and a significant number of early deaths (killing of mature males by immature males) is somehow made acceptable. The problem is, it's easy to break a society; it's extremely difficult to repair it afterward.