If a nomad chooses to settle down as tribal, all nomadic counties will gain a tribe each, and remain under the control of the former nomad. Most government types allows holding of tribes of the same culture, except nomads. There can only be one tribe in a province, but it gets +50% income and levy size for each empty slot in the province. Tribes are the preferred settlement type for tribal rulers, and the only type they can hold without penalties.
