I think in the States, the use of Tribe is still in use as in 'tribal affiliation'. But up here, we use 'Nation' because of certain political measures (like Tripartite Agreements, or Memorandum of Understandings). Most First Nation/Aboriginal communities deal with all 3 level of governments on a government to government basis.

Globally, most Indigenous people are making the push to be recognized as sovereign Nations within nations. It is a loooooooooong uphill fight, but some of us have achieved it (I am thinking of the Navajo Nation in the US and the Nisga'a up here).