Well, their far, far distant relatives were Eastern Asian. Small bands of nomadic hunters from Eastern Asia traveled by foot, in two waves, over the Bering Land Bridge during the last two ice ages, 20,000 and 10,000 years ago. Anthropologists estimated that each band had 50 or so people, but not less. They determined that was the minimum genetic diversity to successfully do what they did, which was spread all through the North American continent and down in to Mexico and South America. The people who built the great Aztec Empire were their decedents.
They remained relatively unscathed until the coming of the Spanish in the 15th century. The foreign diseases wiped out much of the existing civilizations in what we call Mexico today. They also brought them horses, which American Indians didn’t have until then.
Some pockets of “pure” Indian blood remained, hidden in the mountains. Some are still there.
As for the U.S., well, then the White Europeans showed up and all hell broke loose. Indians can live on the reservations if they want, and there are some benefits to it. Most recently, casinos. In Oklahoma you not only go from county to county, there are signs that say, “You are now entering Kaw Nation / leaving Kaw Nation.” or Kiowa or Ponca nations. There are a LOT of native Americans in Oklahoma, but when you hit the Kansas border it seems to end there.
On of my motherless boys, who was my son’s best friend, was part Cherokee. His mom lived in Oklahoma. After living with me for a couple of years during high school, he went on to join the US armed forces. When he made First Lieutenant he teasingly told me I have to call him “Sir.” Ya right. ;)