'Tribe' is as problematic as 'native' is in post-colonial studies.
The politcal reasons informing the argument of these people where
they prefer being refered to as 'tribes' not 'ethnic groups' are that
(and this is just a supposition) what are now nation states are a
conglomeration of tribal states of the past. Each of these, although
existing within the post-colonial state structure, still looks at
itself as a state and any attempt to reduce it to an ethnic group is
seen as an act of attack on its privileged status. Thus, the current
(not suppressed?) demand by some members of the constitional assembly
in Uganda that the country adopts a federal status where power will
rest within specific regions.
Also, in response to another netter who witnessed a contraversial
debate on whether the war in Yugoslavia could be regarded as a tribal
war, it is worth noting that the colonialists loaded the two terms
with new meanings in the context of empire:
`Tribes' only existed in Africa (and the new world) and not in
Europe. And, there were no 'natives' in Europe, just people!!