Captain Jenno said
Red Dead Redemption is a hell of a lot of fun in a posse. You claim a territory, and then shoot anyone with the quads to try and enter it, or you mount an invasion on another group that's already doing it. Killtastic.
I'm pretty sure they have something like this in GTAV too. I haven't tested it yet, but in the menus there's an "Enter Crew Session" option, or something like that. My guess is it puts you and your gang (modern posse) into a map that has other crews (GTAV's name for clans) in it. Viola. Gang wars.
And I gotta say, nothing against RDR, but shooting an Uzi from the window of my mustang or 1980s Camaro and blowing the tires of my target at 80+ mph; is way cooler than firing revolvers and lever actions from horses.
Just my opinion.