It is often repeated that the United States is "a nation of immigrants", implying that we are defined and enhanced by immigrants and should continue to allow significant, diverse immigration. Lets examine the facts.
World history shows that every "nation" is in fact a nation of immigrants. People have migrated repeatedly for the last 5,000 years of history (since the invention of writing). And more than 100,000 years based on anthropology supported by genetics and language development. The earliest moved to unoccupied territory, but most moved and displaced existing populations, and then moved and displaced again and again. As tribes evolved into governments, such migration became immigration or conquest, but otherwise just continued the migration and displacement, again and again. This means that immigration has no special significance.
In North America, research indicates that peoples of Northern East Asia came about 15,000 years ago and settled in Central America, later moving back up into North America. And they too moved and moved again, displacing and replacing prior populations. In the North they were small, hunter-gatherer tribes. To the South there were tribes, but also several large civilizations.
In the early 1600's, Western Europeans came to settle in North America. The French in Canada, and Dutch and English on the East Coast. They were families or commercial adventurers intent on trade. The Spanish and Portuguese had previously settled in Central and South America, but mostly by conquest.
New England was settled by English Protestant families and some Dutch, and the southern coast by English aristocrats. Initially they were just other tribes in the ebb and flow of regional politics, but their advanced food and material production, and consequently population increase, eventually overwhelmed the Amerindian tribal peoples who depended on large territorial claims just to survive.
The "Great Migration" was from 1620 to about 1650. Later immigration up to 1850 was just a trickle. In the late 1700's the colonial population was 95% the descendants of that early migration from England. In the middle 1800's the next big wave came from Western Europe; in the early 1900's from Eastern and Southern Europe; and since 1965 primarily from non-European areas. Immigration was severely limited from 1920 to 1965 to allow assimilation of the earlier waves.
"America", that is the United States, was created primarily by Christian, English immigrants. They came with the English sense of "the rights of Englishmen", the Magna Carta, common law, and the long English struggle with the tyranny of kings. They discovered the America of the Declaration after 150 years of self government. The development of their society was very different from that of the kingly and tribal societies of most of the world.
Later immigrants came for the Liberty and the opportunity that Liberty allows. They did not create it. They prospered in the free air, and strengthened our common history.
But it takes time to adjust to freedom and to abandon the ancient prejudices that conflict with the proven values that allow freedom. Many eventually understand the connection and make the adjustment, but some never do, and some regress to prior prejudices. The ancient enemy, tyranny, is using those prejudices to destroy what we took such trouble to learn, and the immigrants become the enemy of Liberty, and, if they only knew, also their own enemy.