Alright, this might sound crazy, but here goes...
Before the Europeans discovered the Americas, there were many "nations" in the western hemisphere. Even today, we refer to them officially as the Cherokee Nation and so forth.
I think that from an anthropological standpoint, it might be a good learning experience to visit the National Museum of the American Indian, which is located on the National Mall area of Washington DC.
I visited this place one time and let me tell you...it is quite large and covers every aspect of native Americans both before and after the Europeans arrived. I spent a day there and was exhausted by the time I left (actually, it's kind of boring after awhile).
But here is why I recommend it. You can put together a lesson plan based on how these various tribes (or nations) were able to live on the same continent and sometimes share ideas....and other times go to war with one another.
The other thing I like about this is that after the kids are done spending a day at that museum, you should then give them the chance to visit the other museums on the National Mall. There is so much to see in them that it could be inspiring to them in their lives.