The Roman Empire and Inner City Gangs

The other day I was brushing my teeth and it occurred to me- Why don't modern day gangs do the Roman Empire thing? Or for that matter any great Empire thing. These people are so busy shooting at each other that they haven't really examined the idea of joining forces. Just think, (now this isn't an idea that is conducive to the safety of us non-gang people, it's just a curious "food for thought" kind of deal. No, I don't like gangs- in case you haven't sensed the sarcasm yet), but lets say the "Bloods" and the "Crips" combined. In Denver, they are the two biggest gangs. But they aren't the only gangs. If this were like Roman Empire days, they would find a way to conquer or combine with each other so that their territory was SO much bigger. In Denver that would mean that they would control BOTH the West side and the East side of the city. They would be like a SUPER gang. In thinking about this, I can't figure out if that would help lower incidents or raise them. I mean, they wouldn't be going after each other anymore. But there would be many more of them now that they are a SUPER gang. So, the incident rate may rise simply from them being everywhere. I don't know. I'm just saying that I think it's a little strange that there hasn't ever been talk of a merger. That's all.