Although it may sound unlikely, I think it should be "部族の" (a literal translation).

The reason “tribal” is used in favor of the more common and better-understood term "native" (American) is probably that it is used to emphasize the kind of political and cultural identities (including rights and privileges) that a tribal status confers on members within “tribal communities”.

According to this entry of Wikipedia, not all native Americans enjoy tribal status (hence the rights). Quote:

There are 563 Federally recognized tribal governments in the United States. The United States recognizes the right of these tribes to self-government and supports their tribal sovereignty and self-determination. These tribes possess the right to form their own government; to enforce laws, both civil and criminal; to tax; to establish membership; to license and regulate activities; to zone; and to exclude persons from tribal territories. Limitations on tribal powers of self-government include the same limitations applicable to states; for example, neither tribes nor states have the power to make war, engage in foreign relations, or coin money.

…Then there are Tribal Nations that have been denied recognition such as the Muwekma Ohlone[1] and the Miami tribe of Indiana. Many of the smaller eastern tribes have been trying to gain official recognition of their tribal status. The recognition confers some benefits, including the right to label arts and crafts as Native American and they can apply for grants that are specifically reserved for Native Americans.


For more details:
http://en.wikipedia.org/wiki/Native_Americans_in_the_United_... (under “current status”)

http://ja.wikipedia.org/wiki/アメリカ先住民族 (intro on “native Americans in California”, in Japanese)