Since September 11, commentators have claimed on a regular basis that the source of America’s strength is its "diversity." But this is a shibboleth. American diversity is the result of something far more fundamental. The thing that makes the United States unique among the nations of the world is its origin based on a universal idea—the idea of equality as expressed in the Declaration of Independence. It is this idea that has created a racially and ethnically diverse United States—e pluribus unum: one out of many.

The word "nation" comes from the Latin natio, a noun derived from a form of the verb meaning "to be born." "Nation" traditionally has meant a grouping based on such tangibles as race or blood. National movements since the nineteenth century have usually had as their goal the creation of a territorial state encompassing those possessing that common identity. It is this understanding of nationhood that Hitler reflected when he reputedly claimed that the United States was "not a nation (Volk), but a hodgepodge (mischung)." But it is the Declaration, not race and blood, that establishes American nationhood, constituting what Abraham Lincoln called "the mystic chords of memory, stretching from every battle-field, and patriot grave, to every living heart and hearthstone, all over this broad land..."

As Lincoln remarked in 1859: "All honor to Jefferson—to the man who, in the concrete pressure of a struggle for national independence by a single people, had the coolness, forecast, and capacity to introduce into a merely revolutionary document, an abstract truth, applicable to all men and all times, and so embalm it there, that to-day, and in all coming days, it shall be a rebuke and a stumbling-block to the very harbingers of re-appearing tyranny and oppression."

In a speech delivered just after Independence Day 1858, Lincoln clarified the link between the Declaration and American nationhood. His argument is one we should ponder at a time when "multiculturalists" are advancing the view that the US is not a land of free individuals but instead a conglomeration of discrete racial and ethnic groups.

When we celebrate the Fourth of July, Lincoln told his listeners in Chicago, we celebrate the founders, "our fathers and grandfathers," those "iron men...But after we have done this we have not yet reached the whole. There is something else connected with it. We have besides these men—descended by blood from our ancestors—among us perhaps half our people who are not descendants at all of these men, they are men who have come from Europe—German, Irish, French and Scandinavian—...finding themselves our equals in all things. If they look back through this history to trace their connection with those days by blood, they find they have none, they cannot carry themselves back into that glorious epoch and make themselves feel they are part of us, but when they look through that old Declaration of Independence they find that those old men say that "We hold these truths to be self-evident, that all men are created equal," and then they feel that the moral sentiment taught in that day evidences their relation to those men, that it is the father of all moral principle in them, and that they have a right to claim it as though they were blood of the blood, and flesh of the flesh of the men who wrote that Declaration, and so they are."

In Lincoln’s view, America is a nation by virtue of its commitment to the principle of equality, by which he meant simply the idea that no person has the right to rule over another without the latter’s consent. To employ a formulation that was popular among the founding generation, it was not the case that some men came into this world "booted and spurred" while others were "born with saddles on their backs."

For Lincoln, the foundation of American nationhood and the source of the unique character of the United States was the incorporation into the idea of the Union this moral principle of equality. This belief lay at the heart of his opposition to slavery, an affront to the very idea of republican government.

Of course, defenders of slavery such as South Carolina Senator John C. Calhoun, Georgia Senator Alexander Stephens, and Chief Justice Roger Taney and "don’t-care" politicians such as Illinois Senator Stephen Douglas disagreed. Taney and Douglas argued that Jefferson did not mean to include blacks when he wrote that all men are created equal. Calhoun and Stephens contended that Jefferson did mean to so include them but that he was wrong.

The irony is that while Lincoln’s view prevailed with the Union triumph in the Civil War and was subsequently incorporated into the Constitution via the 13th and 14th Amendments, it is the perspective of Taney et al that often holds sway today. The rejection of Lincoln’s understanding of American nationhood is especially visible in the quest for "diversity" as an end in itself.

"Diversity" is the poisonous fruit of that toxic doctrine, "multiculturalism." The latter—the discredited idea that race defines destiny and that blood determines who we are—would appeal to Hitler. Multiculturalists reject the principles of the Declaration because they see them as, at best, "cultural imperialism" and at worst, racism.

In America, ethnicity is an indicator of whence we have come, not whither we are going. It is precisely by rejecting ethnic politics and embracing politics based on individuality and equality of natural rights that have created the conditions of civility and domestic tranquility upon which American strength and prosperity rest. The increasing hyphenation of America bodes ill for these conditions.

It is, of course, a cliché to observe that America is a nation of immigrants. And while immigrants often have kept the memory of the old country alive, the vast majority came to the United States to become Americans.

Of course, the Founders did not believe, as do some of today’s liberals, that there is an absolute "right" to immigration and US citizenship. They held that since America is a polity based on consent as well as equality, citizens have certain rights against foreigners, one of which is the right to exclude immigrants based on a judgment regarding the character of those to be admitted. For instance, members of a particular religious sect might be rejected if that religion’s beliefs are fundamentally at odds with the principles that lie at the foundation of republican government.

But the Founders did not fear "outsiders" per se, demanding only that they abide by the law. As Washington wrote in 1790 to the Hebrew Congregation of Newport, "...happily, the Government of the United States, which gives to bigotry no sanction, to persecution no assistance, requires only that they who live under its protection should demean themselves as good citizens...."

The emphasis on diversity as an end in itself undermines republican government by "balkanizing" American citizens and pitting ethnic groups against each other in an endless quest for victim-hood. September 11 should impel us to reject the ethnic warfare implied by multiculturalism and diversity, and to reflect on the foundations of American nationhood that are to be found in the Declaration of Independence. Of course, as the sad history of slavery attests, we have not always lived up to the "self-evident truths" articulated in this document. But these truths constitute what Lincoln called the "central idea" of the American Republic without which republican government will fail and the American nation will dissolve. This is the real meaning of America, and in the wake of September 11, we need more than ever to rejuvenate our central idea.

Mackubin Thomas Owens is professor of strategy and force planning at the Naval War College in Newport, RI, and an adjunct fellow of the Ashbrook Center. The views expressed here are his own and do not reflect the position of the War College, Navy Department, or Department of Defense.