A gang is just a group of people who organize around a set of rules or beliefs and is considered to be illegal because they are operating outside the limits set by the current regime. Let's use the Taliban as an example. Some people called them a terrorist organization that was by intents and proposes a gang. So when they are now called the Islamic Emirates of Afghanistan, and are recognized as the government leaders of Afghanistan, they no longer are performing illegal acts, because they make the laws. If an organization turns to seize control we change the name from gangs to rebel groups. Then rebel groups to government.