Researching her new book “Caste: The Origins of Our Discontents” so disturbed Isabel Wilkerson that its acknowledgments thank the music that helped her get through it.

The follow-up to Wilkerson’s National Book Critics Circle-winning “The Warmth of Other Suns” details how our country codified a system that insists on the inferiority of “subordinate caste” people, depriving them of employment, economic opportunity, dignity and, sometimes, their lives.

“Caste” compares the United States to India, whose “untouchables” are useful for everyone else to look down upon. And it shows how the Nazis studied the Jim Crow South for tips on how to eradicate their “subordinate caste.” Except the Nazis found the U.S. system too harsh.

Wilkerson, a former reporter for the New York Times who will participate in a virtual Talking Volumes event Tuesday, began using the word “caste” in “Warmth,” her 2010 book about Black people’s Great Migration to the North. She thought the term described better than “race” the arbitrary divisions such as skin color and country of origin that are used to categorize us.

As she describes it, “caste is the bones, race is the skin” of American inequality.

“I was using the word all the time, in every talk, to describe the experience of people who fled the Jim Crow South, a place where it was against the law for a Black and a white person to marry, or play chess together in Birmingham,” said Wilkerson, by phone from her home.

The resulting book, labeled “an instant American classic” by the New York Times’ Dwight Garner and maybe “the most important book I’ve ever chosen for my book club” by Oprah Winfrey, seems destined to change the way we grapple with race — although “racism” is a word Wilkerson uses never in “Warmth” and only rarely in “Caste.”

A new way of understanding

The book came about gradually, as Wilkerson wrote about events such as the shooting of Trayvon Martin by a white vigilante in Florida, the killing of Philando Castile by a Minnesota policeman and a white man’s murder of worshipers at a Charleston, S.C., church.

In a way, the book’s subject found her.

“I’m the type of writer who is always taking notes, writing down ideas,” said Wilkerson. “Then Charlottesville happened [the deadly white-supremacy rallies in 2017] and it was really clear to me that this warranted something on its own, something that would go deeper and be more expansive to get underneath what we are seeing.

“The idea of caste gives us new language to understand these divisions in a different way than we are accustomed to. We’re not dealing with the classical open racism of our forefathers.”

Wilkerson, whose writing and conversation reveal her gift for metaphor, describes America as an old house and herself as a building inspector providing a report on the structure’s health. It’s not a favorable report.

“It’s in some ways an X-ray of our country that allows us to see the underlying structure. You can’t see the joist and the beams. You know they’re there because the building is standing. But you can’t see stress cracks, the unevenness of the beams. This allows us to see that the building will not be sound unless the structure is sound.

“It’s a way of looking at any country, any institution,” she added, agreeing that this includes the Star Tribune, which is currently examining its own structures of inequity.

The system doesn’t just damage those at the bottom of the pecking order. Wilkerson insists that caste structures hurt all of us.

“People who are the targets of the caste system bear the brunt — and often assault — of being assigned to the bottom of this hierarchy. But there are costs to everyone, to the entire society, because of the distancing and the fractures to society,” said Wilkerson.

“Because of the divisions and the walls that have been built between us going back for centuries, we do not necessarily understand or feel called upon to see we have a stake in everyone in our country — that we have more in common with one another than we were led to believe.”

Like assembling a quilt

Structure was also a major concern with “Caste,” with Wilkerson constantly reshuffling chapters, which include personal reminisces, interviews with people whose lives have been defined by caste, historical material and her own analysis.

Comparing the way she assembled the manuscript to quilting, Wilkerson said she color-coded the various elements, knowing that moving any section would require shifting others so that each piece flowed from the last and into the next.

She even posted an Instagram a photo showing her multihued manuscript.

“The ultimate goal of all of this is to help us recognize that these divisions were created and that, if they were created by humans, they can be resolved by humans,” she said.

Shifting from quilter back to building inspector, Wilkerson points out that not only must America’s HVAC be repaired, but there’s a crack in the foundation. And is that a leak in the roof?

“It’s not one thing,” she said. “It’s an ongoing challenge. You roll up your sleeves and get to work and you get it done.”

Immersing herself in lynchings, enslavement, Jim Crow and the Holocaust sent Wilkerson to meditation and to musical favorites for respite, with Philip Glass, the Police and the “Diva” soundtrack among her go-tos.

She acknowledges her playlist and offers a call to action at the end of “Caste,” declaring that “the price of privilege is the moral duty to act when one sees another person being treated unfairly.”

Wilkerson believes the time to act is now and that “dominant castes” must be part of it.

“The more resources an individual has, the greater impact they can have,” she said. “It’s so much bigger than any one person, any one group. This is a challenge for the species, to find a way to transcend the artificial boundaries that have been in place for so long that we see them as a normal part of the social order.”

Her book illustrates the challenges faced by those in “subordinate castes” who try to change things, Wilkerson herself included.

She writes about a conference to which she was invited because of the success of “The Warmth of Other Suns.” Another attendee, a scholar from India, asked her what caste she is in.

Wilkerson was taken aback by the question, which she had not pondered. But the bestselling writer, Pulitzer Prize winner and former journalist of the year replied that she is at the very bottom.