A nation consists of people with potentialities and proclivities derived from their objective, biologically given natures. A nation isn't filled with abstractions, doesn't exist for the sake of abstract ideals, and changes when the makeup of its inhabitants change. Europeans in Africa created European societies. Africans in Detroit have created an African society.
Humans are not all the same and are not infinitely interchangeable. The global egalitarian idealization of all people as one is at odds with nature's diversity and with what the Founders intended the republic to be.
Here's what Benjamin Franklin wrote in a 1751 essay entitled "Observations Concerning the Increase of Mankind":
"The Number of purely white People in the World is proportionably very small... I could wish their Numbers were increased... Why increase the Sons of Africa, by Planting them in America, where we have so fair an Opportunity, by excluding all Blacks and Tawneys, of increasing the lovely White and Red? But perhaps I am partial to the Compexion of my Country, for such Kind of Partiality is natural to Mankind."
In 1821, Thomas Jefferson wrote as follows in reference to the freeing of African slaves: "Nothing is more certainly written in the book of fate than that these people are to be free. Nor is it less certain that the two races, equally free, cannot live in the same government. Nature, habit, opinion has drawn indelible lines of distinction between them. It is still in our power to direct the process of emancipation and deportation peaceably and in such slow degree as that the evil will wear off insensibly, and their place be pari passu filled up by free white laborers."
This is consistent with the 1790 Naturalization Act, which set forth the following qualifications for citizenship: a free white person of good character who has lived in the United States for two years.
Life, liberty, and the pursuit of happiness does not translate into "Give me your tired, your poor, Your huddled masses yearning to breathe free, The wretched refuse of your teeming shore." Life, liberty, and the pursuit of happiness pertains to the lives, liberties, and happiness of the particular subset of the world's population that is fit to be called citizens of the United States.