Add at least three separate gangs to each city, with their own randomized membership, organizational structure, turf, and money making ventures, using the already pre-existing money lenders and illegal arms and drug dealers and making them affiliated with one gang or another, and make it so they have random relationships with each other, with some forming alliances and others being rivals. Turf would ideally shift via wars and buyouts over the course of the game, with gang warfare being a quite simple affair of “some guys start shooting at other guys in the streets”.
In addition, as the name implies, let some murders be related to mafia squabbling, with murders potentially increasing tensions between the gangs if one gangster kills a rival gangster, or even some Yakuza plotline shit where a gangster tries to murder one of their own and pins it on a rival gang in an attempt to start a gang war.