At lunchtime Monday, shortly after he heard that the once-mighty Sears company was filing for bankruptcy, Louis Hyman thought, “Huh, I should write some stuff down.”

Hyman, a historian of capitalism who teaches at Cornell University, spent 10 minutes or so typing out a Twitter thread that began:

“In my history of consumption class, I teach about Sears, but what most people don’t know is just how radical the catalogue was in the era of Jim Crow.”

He added a few more thoughts, about how the old general stores in the rural South, run by white people who often treated black customers poorly, reinforced the white supremacist hierarchy.

“Every time a black southerner went to the local store they were confronted with forced deference to white customers who would be served first,” he wrote.

He went on:

“The catalog undid the power of the storekeeper, and by extension the landlord. Black families could buy without asking permission. Without waiting. Without being watched. With national (cheap) prices!”

Several tweets later, he headed off to teach a class.

When class was over, Hyman wondered if anyone had paid attention to his mini-tutorial. He checked Twitter.

“Oh my God,” he thought.

Until that moment, the closest he’d come to a blockbuster tweet was a favorable New York Times review of his latest book, “Temp,” about the corporate forces behind the gig economy. It had been shared 40 or so times.

But now? A few hundred people had retweeted his thoughts on how the Sears catalog helped to upset white supremacy. By Tuesday, that number had surpassed 15,000.

“I think Americans aren’t very aware of how Jim Crow worked,” he said when I tracked him down by phone to talk about his tweets and the overwhelming response.

Jim Crow was the system that enforced racial segregation in the American South for nearly a century after the Civil War. The Jim Crow laws not only separated blacks and whites — at lunch counters and water fountains, in movie theaters and elevators and buses — it relegated black people to lesser spaces and opportunities. Shopping was just another element of the oppression.

“Jim Crow was a very dark time in our past,” Hyman said. “It was also a time of tremendous contradiction.”

The contradiction lay in the fact that the white supremacist order relied on the labor of African-Americans.

“But if you pay people,” he said, “how do you get that money back into the system?”

The mail-order catalog was one circuitous route.

“The catalog was a real opportunity for African-Americans to evade this racist monopoly they encountered on an everyday basis,” Hyman said.

In response to the Sears catalog’s popularity, some shopkeepers held catalog-burnings in the streets. Country stores often served as post offices and some shopkeepers refused to sell African-Americans the stamps needed for a catalog order.

To deter whites from supporting Sears, rumors were spread that the company founder, Richard Sears, was black. To reassure white customers, Sears published a photo showing he was white.

Despite the storekeepers’ backlash, the catalogs kept coming and customers, black and white, kept buying. By the mid-1960s, Jim Crow was officially dead.

“This is part of the long story of the black struggle against Jim Crow,” Hyman said, a quest for economic equality that was, and remains, tied to the struggle for political equality.

I asked Hyman if he’d received any hate mail about his tweets. To his surprise, he said, he hadn’t, though some white people have wondered, “Why are you always talking about race?”

The full story of the Sears catalog isn’t only about race, but Hyman’s Twitter tutorial shows how even things not widely associated with race may be tangled in it.

His history lesson has applications for modern times too.

“It’s easy to think of buying a thing as an innocuous act,” he said, “but it’s always embedded in social meaning.”

He said some transgender people have responded to his tweets by noting that they use the internet in much the same way African-Americans once used the Sears catalog, so that they can buy what they want with a sense of safety and privacy they may be denied in a store.

Hyman points out that who gets to buy what, and under what conditions, remains an important question.

“There’s power in the catalog,” he said. “There’s power in the website.”

And as he put it in his Twitter tutorial:

“So as we think about Sears today, let’s think about how retail is not just about buying things, but part of a larger system of power. Every act of power contains the opportunity, and the means, for resistance.”

Mary Schmich is a Chicago Tribune columnist.