Source: (2005) In, Nielsen, Marianne O. and Zion, James W., editors, Navaja Nation Peacemaking. Living Traditional Justice. The University of Arizona Press. Tucson pp.171-176

Today, in the United States, we have three types of sovereign entities – the federal government, the states, and the Indian tribes. Each of the three sovereigns has its own judicial system, and each plays an important role in the administration of justice in this country. The part played by tribal courts is expanding. As of 1992, there were about 170 tribal courts with jurisdictions encompassing a total of perhaps one million Americans. (excerpt).