The Internal Revenue Service has special tax laws in place for tribes that are advantageous, beneficial to their standing. There are approximately 600 sovereign tribal nations across the United States. These are all recognized by the Internal Revenue Service as tribal governance. Tribal governments are unique members of the American government. These tribal nations are sovereign governments, similar to that of Canada.
Tribal governments have the ability to act as their own entity. They maintain power, they can determine their own government structure, pass their own laws, enforce them, etc. Tribal governments have access to a lot of federal programs, but not all in line with state and local governments. Instead, what they have access to is the ability to self-govern, be independent. The Internal Revenue Service recognizes them as entities, as their own organizations, and treats them as such with special tax treatment across the board. This tax treatment is beneficial to their economies in the short and long-term.