A number of years ago in a television interview the political commentator George Will asserted that being an American is, unlike the identities of the European (and other) nations, based on the concept of assent. This means, in short, assent to or acceptance of values in the primary documents of the United States, namely, the Declaration of Independence, the US Constitution, and the Bill of Rights. By contrast, Will stated, other peoples throughout the world trace their roots or the essence of their nationhood to a distant past without an explicit concept as its foundation except that of ancestry and language—which in some sense merely begs the question of what their nationhood means.
Without necessarily agreeing with George Will's right-wing political views, we can see that on this issue he's expressing a truth, but one without specifics beyond his mention of the primary documents, which many Americans probably have never actually read. We also must deal with the fact that the actual history of the US would have been quite different if most Americans had actually believed the core truth expressed in the Declaration that "all men are created equal." We can, however, hope that a greater percentage of Americans believe in this eternal principle now than at any earlier time in our history, despite the xenophobia that has been encouraged in political demagoguery at the highest level over the past several years. We will therefore conclude that the principle of equality is the potential and intended essence of Americanism, though it has been very (to put it mildly) imperfectly carried out.
But if we were to choose a specific point in the primary documents that we can say Americans as a whole probably have consistently based their national identity on, in my opinion it would be the following:
We, therefore, the representatives of the United States of America, in general Congress assembled, appealing to the Supreme Judge of the world for the rectitude of our intentions, do, in the name and by the authority of the good people of these colonies, solemnly publish and declare that these united colonies are, and of right ought to be, FREE AND INDEPENDENT STATES...[Italics added]
This one sentence seems to encapsulate a series of key points that have defined, and still define, the American psyche and even can be said implicitly to establish the conviction of the equality of mankind. If we break it down point by point, it asserts 1) the different states are united, 2) the government is a representative one, 3) it is founded at least implicitly on the concept of a higher power that judges us, without reference to or accepting any specific religion or necessarily any organized religion at all, and 4) the United States are/is free and independent in perpetuity.
I italicized the one clause for two reasons. First, it was not written by Jefferson himself but added by Congress before the document was finalized (though it is not inconsistent with the deism of Jefferson and others). Second, judging by the thinking and intentions of Americans throughout history, the clause contains what might be even more central than the other points we've noted. It expresses both the idea of belief in a power greater than humanity, and the non-requirement of a specific belief beyond this generalized one. It also asserts that Americans themselves base their new country on "the rectitude of our intentions." The intention is, and has been for 243 years, to do right, however imperfectly it has been realized.