A gang is a family of real players under a Don. You can join one from your first days or start your own, recruit, and give it a name, a tag and a home district. Every gang has ranks, from soldier up to the Don, and its own page where the whole family is listed.
Members chip in to a shared treasury and a vault for items, with a ledger so everyone can see where the money went. The Don and the trusted ranks decide how it is spent. If a Don goes quiet for too long, the next in line takes over, so a family never dies with an absent boss.
Gangs earn respect and climb the rankings. When two families can't share the streets, they go to war: the war is scored, both sides fight for it, and it ends on terms. Win and your name grows; lose and the whole city reads about it.
Your gang is also your company: send mail, plan together, back each other up in fights and bust each other out of jail. Gangs are based in the districts they call home, and the newspaper follows the biggest families.
Joining is simple: find a family that is recruiting and ask to join, or start one yourself when you are ready. The gangs list shows every family in town, where it is based, how big it is and how much respect it has earned, so you can pick a side before the trouble starts.