The Collaborative International Dictionary of English v.0.48:
Tribalism \Trib"al*ism\, n. The state of existing in tribes; also, tribal feeling; tribal prejudice or exclusiveness; tribal peculiarities or characteristics. [1913 Webster]WordNet (r) 3.0 (2006):
tribalism n 1: the state of living together in tribes 2: the beliefs of a tribal society