Any people who live a mobile existence can be considered nomads. They survive by moving to wherever the resources are. Some nomadic tribes or bands are racially diverse, and others are racially homogeneous. A few tribes enjoy the sponsorship of (and provide services to) a patron, such as a city-state, but most survive independently by herding, hunting, or raiding. A single tribe might resort to all of these methods.
Survival on the move isn’t easy. Some tribes, especially those made up of raiders, aren’t shy about taking what they need from established locals and strangers. Slave tribes raid outlying city-state holdings and caravans in a guerrilla war against their former oppressors, and bandits prey on whomever they perceive to be weak. Most other tribes – those that consist of herders, hunters, merchants, or scavengers – are more likely to trade than to steal.
Like independent villages, nomadic tribes usually have strong leaders who boast military or magical skill. Unless tradition forbids the use of magic, most nomads tolerate it, along with other practices that would get one killed within the borders of a city-state, such as defying authority.