Originally a big nation with a population of tens of millions, why did it directly become a minority in less than a hundred years?

This nation used to be a big country with a population of tens of millions, but in just a hundred years, it has changed from tens of millions of people to ethnic minorities, that is, Indians. Before the European invasion, Indians were a big race. The population once reached tens of millions. In fact, their ancestors were just a few hundred people chasing mammoths across the Bering Strait. From this, we not only feel the development of Indians. But all this stopped with the arrival of European colonists. When the British immigrated to North America, they were native Indians. In fact, it has helped this group of foreign Europeans a lot. However, with more and more British people coming to North America, white people's attitude towards Indians began to change from friendliness to deterioration. British colonists or British immigrants are far less generous to the aborigines and Indians, but bite the hand that feeds them. Slaughter Indians and aborigines. When the United States was developing the west, the atrocities against Indians reached a climax again. This behavior of the United States was naturally resisted by indigenous Indians. This hindered Americans from developing to the west. Under the powerful force of the United States, the only way for the Indians in the west to survive is to surrender. In this atrocity from America, most Indians died. In today's 2 1 century. At first there were about 30 million Indians in the world. But today, Indians only account for about 1.2% of the total population of the United States. And this 1.2% is not all Indians. 1.2% of the data sources include both indigenous Indians and some mixed-race descendants. Most of the descendants of these hybrids are descendants of colonists among local indigenous women!