I have many problems with this map, notwithstanding the fact that dozens upon dozens of tribal groups are combined into monolithic nations.

Nations that Ought not to Exist:

As /u/PastelFlamingo150 said, why do the Olmec still exist?

In a particularly glaring example, the Comanche didn't emerge as a people until they acquired horses in the 17th century, and so ought not to exist at all.

The Anasazi vanished in the 12th century, so I'm not sure what they're doing here.

European-Driven Migrations

The Cheyenne lived in Minnesota when the Europeans arrived, and only moved west when forced by tribes with firearms.

In a similar error, the Crow lived by Lake Erie and only moved west when better-armed neighbors forced them to do so.

Location Errors:

Why do the Chickasaw live in Texas, when their historic land was in Tennessee, Mississippi, and Alabama?

Why are the Creek in Florida when they lived along rivers in Alabama and Georgia?

Why are the Beothuk given a portion of the mainland when they exclusively lived in Newfoundland?

Why have the Objibwe moved from Sault St. Marie and Lake Superior to the Chicago area?

Why have the Mahicans moved from upstate New York and western Massachusetts to Maine?

The Dogrib live north of Great Slave Lake, not south of Lake Athabasca.

Just like the Dogrib, the Slavey have been moved from their home around Great Slave Lake to south of Lake Athabasca.

Other Error

The Flatheads and the Salish are the same. "Flathead" was the original European name for them, while Salish is what they call themselves.

Edit: I have been informed that this map was made for /r/imaginarymaps, so keep that in mind. I may have been a bit harsh, as I assumed it was a serious historical attempt at what an uncolonized North America would look like.