Tribalism is one manifestation of a force of collective assertion, aggression and defence that is also inspired by race, religion, communal identity, a communal commitment exalted in some nations as patriotism. It is the primal urge to belong to one group and hate the rest.
The most common face of tribalism is uncouth and uncivilized: from warring tribes in Africa to hooded Klan members in the USA, from fanatics in the Indian subcontinent to mass murderers in Bosnia, from jeering skinheads in Germany to the desecrators of Jewish graves in France. Designer tribalism is understated. It lies unexpectedly beneath the surface of societies with high standards of living and generally long exposure to democratic practices. It begins to reveal itself when official responses to fascist violence exhibit an alarming tepidity; when the violence is seen as basically a law-and-order problem and not an act of terrorism; and when members of the racist fringe begin to move into the political mainstream.
A tribe is a family which has grown as a result of procreation. It is a big family; it provides its members with material benefits and social advantages the family provides for its members. It is a natural social umbrella for social security, bringing up children and providing a sense of identity.