First off the scenario is unlikley to happen. White gangs are typically racist and have ties to white supremacist militias who will help them. The United States is not homogenous country where the general public could unite to ovverthrow the govt. There is so many different opinions and different goals different political ideologies that wouldnt happen. Gangs wouldnt represent the people they would actually be the opposite. They would be agents to divide. Gangs are only driven by money and if the govt descided to put out a 300 billion dollar program for gangs to fight against the people they would take it. That was how the US military did to defeat ISIS when they were AQI(Al Qaida in Iraq) back in the insurgency days in the mid 2000s. They paid Sunni tribes huge amounts of cash to fight against ISIS. That is why when ISIS took over last year they killed the same Sunni warlords that turned against then wholesale. Gangs arent trained in firarms,do not know how to grow food,do they have international contacts to get weapons? For an insurgency to suceed they need external and internal support. In the black community contrary to cac conservative media we do not support gangs and actually see them as bandits in the community.
Example of different races banding together.- say everyone mutually agrees we don't like each other or whites don't like no one, but that the current system is bad. Maybe each group agrees to take a region of America after the takeover. And if shot gets bad enough in America people might prefer gangs over government. It's a common saying for some that they "preferred when the mob ran the streets over the police"