This is the reason we celebrate Independence Day on the fourth of July rather than on the second.
Jefferson's Declaration began as simply a political document announcing the separation from Britain and the birth of a new independent nation. It has become much more than that. It is now an American creed, assuming an almost religious significance about what we believe as Americans: liberty, equality, and republican government. And in the absence of traditional components of nationality, those ideas in the Declaration of Independence have become a substitute for those components. It is the ideas of the Declaration of Independence that to a large extent constitute our national identity.
Traditionally, any people's national identity rests upon geography, language, ethnicity, and religion. People groups generally identify with some geographic location where they have lived. Regardless of how well their land has provided material needs, they romanticize it as their homeland. They lay some claim to it based upon historical or mythological narratives about how they settled there. They are unified by a common language. Speakers of other languages are often seen as less civilized. Perhaps the linguistic group share some physical characteristics that encourage the development of some degree of ethnic consciousness. Finally, a shared religious tradition adds to their social cohesion and provides myths about origins and destiny Often their government provides legal and financial support to their historic faith.
These traditional elements of national identity only had shallow roots in the New World. Over the two centuries of our history as an independent nation, there roots have withered. First, America’s sense of place is not as deep rooted as that in other nations. Many of the first settlers, especially the wealthier leadership behind the colonization efforts never intended to make North America their permanent home. They hoped to strike it rich like Spanish conquistadors and return home to Britain to assume the life of country gentlemen. The few that achieved this goat were largely the sugar planters in the islands of the West Indies. Most of those who come, however, never became prosperous enough to make it back home to Britain. For others, the North American wilderness offered opportunities for the future, not a basis for a historic homeland rooted in the past.
Second, Americans do not have their own language. We speak a foreign language: English. Even the regions accents of American speakers of English derive from the different regions of England from which they originated.
Third, Americans does have a distinctive ethnicity identity, especially when considered from the perspective the physical appearance. Europeans, Africans, and Asians all differ in degrees regarding aspects of physical characteristics. And the people of many nation-states to some extent exhibit the physical characteristics of the dominant ethnic background. We all have some general expectations of how persons form China, Nigeria, or Italy appear to us. Not so much with Americans. No one recently has expressed surprise upon meeting someone by saying "Funny, you don't look American.".
America to a higher degree than most other nations is known for its ethnic diversity. Out diversity is hardly a recent development. Britain’s colonies from the beginning possessed a diverse population. Europeans from Britain, Sweden, Holland, Germany, and France established enclaves of settlement. Africans from that continent’s West Coast lived throughout the colonies, though chiefly in the Southern region. A general sense of Northern European identity that Americans shared gradually disappeared with the later arrival of Eastern and Southern Europeans, Asians, and in more recent times, Hispanics. Because of this immigration and ethnic diversity, Americans possess no distinct physical characteristics of an ethnic group.
Finally, America has no national, government supported religion. This circumstance, too, results from our long standing diversity. Anglicans, Congregationalists, Presbyterians, Quakers, Dutch Reformed, Baptists, Lutherans, Unitarians, and Deists populated the early colonies. Some colonies established a particular denomination as the government sanctioned faith. This resulted in some persecution of Quakers by Congregationalists in Massachusetts, and of Baptists in Virginia by Anglicans. Partly because of this religious diversity, the Constitutional Convention created no nationally established religious denomination. The Constitution of 1787 left the legal status of religion to the states. Gradually, however, even the state establishments disappeared. Americans shared a general sense of Protestantism (that accompanied their self-conception as ethnic Northern Europeans) for many decades. The immigration that brought new ethnic groups also brought new religious faiths. Adherents to Catholicism now outnumber any Protestant denomination and a wide range of non-western religious faith now dot the cultural landscape.
So what holds such diverse elements together? The ideas contained in the Declaration of Independence. The devotion to the ideas of liberty, equality, and republican government provides the cohesion that in many other diverse countries can only be achieved through authoritarian governments.
As historian Richard Hofstadter put it, "It has been our fate as a nation not to have ideologies, but to be one."
In other words, we are not Americans because of who we are geographically, linguistically, ethnically, or religiously. We are Americans because of what we believe.