Tribalism, in Benjamin Barber's book Jihad vs. McWorld: How Globalism and Tribalism are Reshaping the World, refers to militant ethnic groups eager to protect themselves from "the other", be that another tribe, or modernization, or Western popular culture. In a broader anthropological context, it has been used euphemistically for "primitive." 
More generally, it is a group identity that could be held even within a modern society. It does not require living in a tribal social structure.
- Benjamin Barber (1996), Jihad vs. McWorld: How Globalism and Tribalism are Reshaping the World, Ballantine, ISBN 034538304, pp. 8-12
- Nigel Rapport, Joanna Overing (2000), Social and cultural anthropology: the key concepts, Routledge, ISBN 9780415181563, p. 364