I have found tons of results about wars between natives and the US (et al.) government, but I would like to read about conflicts between tribes beyond very simple descriptions. Some things I am particularly interested in: Did Native American tribes have professional soldiers? Were fortifications used? Were large scale battles fought (several thousand people)?
Thank you!
I can't answer your questions in depth, but as a Native, I can offer some insight.
We're not a monolith. Our cultures, customs, and histories vary greatly. You would do well to look into specific nations and their histories if you wish to know more, but blanket statements such as this usually aren't going to get you the result you're looking for.
Many native nations have a different mindset of war that differs from the traditional usage. For example, many southeastern Mississippian cultures utilized stick ball as a form of war, but it was just as "final" as who won a battle.