Identity politics—the artificial segmentation of Americans into antagonistic groups organized along often imagined ethnic, racial and sexual categories—is tearing America apart. President Trump can do something about it.

Government played a key role in creating these identities. The establishment of a new official taxonomy of Americans started roughly in 1966, when the Equal Employment Opportunity Commission began asking companies with more than 100 employees to collect information through the EEO-1 form on “Negro, American Indian, Oriental and Spanish-surnamed” employees. What began as an effort to track how policies affected people thought to be disadvantaged easily but tragically slid into government-sanctioned promotion of victimhood and racial preferences. The goal of the Civil Rights Act of 1964, to prohibit racial discrimination, was turned on its head.

“The EEO-1 was a public, if implicit, federal declaration of the nation’s minorities,” writes University of California, San Diego political scientist John Skrentny in his 2002 book “The Minority Rights Revolution.”

“Being listed on the EEO-1 was a crucial prerequisite for benefiting from a difference-conscious justice,” he concludes. “Without much thought given to what they were doing, [policy makers] created and legitimized for civil society a new discourse of race, group difference and rights. This discourse mirrored racist talk.”

Spurred by lobbying from liberal advocacy groups, in 1977 the Office of Management and Budget standardized the categories of “white, black, Hispanic, Asian and American Indian and Alaska native” nationwide. Added to the two familiar races, black and white, were three incongruous pan-ethnic categories. The Census Bureau went ahead and carved the entire country into what social scientist David Hollinger has dubbed “the ethno-racial pentagon.” Starting in 1980 the census began tabulating all residents into groups that correspond to a vague and unscientific color code: white, black, brown, yellow and red.

If you don’t think of yourself that way, the government will do it for you. There’s a box on the census for “some other race,” but the bureau explains: “When Census 2010 data were edited to produce the estimates base, respondents who selected the Some Other Race category alone were assigned to one of the OMB mandated categories.”

For people who tick multiple boxes—permissible since 2000—OMB has instructed the Census Bureau to “allocate” responses that “combine one minority race and white” to “the minority race.” As Mr. Hollinger puts it, “thus the federal government quietly reinserted into the tabulation of the census the principle of hypodescent”—the technical term for the old segregationist one-drop rule—“that the opportunity to make ‘more than one’ was publicly said to repudiate.”

Until the Trump administration stopped it last month, the census was preparing to add in 2020 yet another vast pan-ethnic grouping—“Middle East or North Africa”—for residents with ancestry anywhere between Morocco and Iran. That would have made a minority of everyone from Rep. Darrell Issa to the late Steve Jobs.

Every level of American government now follows this scheme, as do most other major institutions. Public schools promote the invidious idea that all subjects, even math, should be taught differently to children depending on where administrators place them on the pentagon. Universities have become cultural battle zones where students search for victim status rather than truth. And if you work for a large organization, there’s someone in your human-resources department whose job is to put you into one of the government-created silos.

What can be done about all this? Mr. Hollinger has proposed to do away with the pan-ethnic groups altogether and “count instead those inhabitants who identify with descent communities from specific countries.” The 2020 census starts down that path by adding a “write-in area” for countries of descent for both whites and blacks, as well as Hispanics, but will still divide them under the pan-ethnic umbrellas.

Sociologist Nathan Glazer, co-author with Daniel Patrick Moynihan of the classic 1963 study “Beyond the Melting Pot,” has similarly proposed asking only questions on national descent, and going back only as far as grandparents, “because by the third generation and certainly the fourth, the mix of ethnicities is extensive,” as he wrote in 2002.

Such revisions “would indicate that the census and the government are not interested in group characteristics in the third generation and beyond,” Mr. Glazer wrote. It would also be consistent with censuses at the turn of the last century, when there was also a high percentage of Americans of foreign birth, and the census asked questions on origin and citizenship (the latter of which is being considered for reintroduction in 2020).

Messrs. Glazer and Hollinger agree on retaining a question about whether a resident considers himself black. Mr. Hollinger’s solution is to include a box labeled simply “African.” As Mr. Glazer puts it, “this is the group that has suffered from prejudice, discrimination, and a lower caste status since the origins of the republic.”

The Commerce Department must submit 2020 census questions to Congress by the end of next month. Mr. Trump should issue an executive order directing the OMB to rescind the 1977 directive (and a 1997 revision) and the Census Bureau to abandon pan-ethnic categories in favor of a question about national origin—either fill-in-the-blank or a box for every country in the world, from Afghanistan to Zimbabwe.

The order should further instruct all federal agencies to root out the collection of this faux data—which occurs internally throughout the executive branch and is forced on states and government contractors through federal policies and regulations. Mr. Trump could instruct agencies to report back on their progress after, say, six months.

“It is necessary and desirable to recognize and encourage the ongoing assimilation of the many strands that make up the American people into a common culture,” Mr. Glazer wrote. “One encourages what one recognizes and dissuades what one does not.” Mr. Trump has an opportunity to encourage unity and dissuade the division of Americans by race and ethnicity.