The continent,or a large section such as the U.S, was never unified as a single entity under a single tribe. There were disputes of territories for hunting and fishing. Agreements changed over time between various tribes. Typically the name that a tribe or group of tribes called themselves translated as "the people" in their language. Other tribes were not referred to as the same.
There were cases of one tribe wiping out another and taking over their land. The same thing happened when the whites came. The had better technology, weapons, and greater numbers.
Some groups welcomed the Europeans, some attacked them.
Sometimes when the U.S. government forced different tribes into a common reservation, traditional enemies were forced to live together.
The Europeans had the technology and the ability to work cooperatively to form a government that could control such a large section of land.
Oh, didn't you know? We still have our own tribal nations, and we DO control who can come into our territory. For example if you were selling drugs or were violent, etc. you could be banned from the rez. There are even tribes that are stripping their own citizens of their tribal membership and banning them from the rez (e.g. for selling drugs). They also don't allow squatters to just set up camp on a rez, they will be evicted and/or escorted off as well.
By the way, there are over 500 tribal nations, but we also have dual citizenship - we are US citizens as well. We don't "set" US immigration policy because of our indigenous status, we participate in the political process like everyone else. The USA is actually a nation that exists, son. And there is a southern border. Oh yeah, and Mexico is a nation that exists as well, and they keep their southern border locked out tight too. There is no right for people with indigenous ancestry to cross all modern national borders in the Western Hemisphere. I know that is your agenda, but that's not how it works. An Alaska Native can't just say he is indigenous and head down to Mexico and demand that the borders be open to him and he should have Mexican citizenship also.
You are not a Native American unless you are a citizen of a tirbal nation. It has been that way since the first White set foot on these lands and it has CONTINUED to be the case. It will always be that way.