Most Americans know that George Washington owned enslaved people at his Mount Vernon home. But fewer probably know that it was his wife, Martha, who dramatically increased the enslaved population there. When they wed in 1759, George may have owned around 18 people. Martha, one of the richest women in Virginia, owned 84.

The high number of people Martha Washington owned is unusual, but the fact that she owned them is not. Stephanie E. Jones-Rogers, a history professor at the University of California-Berkeley, is compiling data on just how many white women owned slaves in the U.S.; and in the parts of the 1850 and 1860 census data she’s studied so far, white women make up about 40 percents of all slave owners.

Slaveholding parents “typically gave their daughters more enslaved people than land,” says Jones-Rogers, whose book They Were Her Property: White Women as Slave Owners in the American South came out in February 2019. “What this means is that their very identities as white southern women are tied to the actual or the possible ownership of other people.”

White women were active and violent participants in the slave market. They bought, sold, managed and sought the return of enslaved people, in whom they had a vested economic interest. Owning a large number of enslaved people made a woman a better marriage prospect. Once married, white women fought in courts to preserve their legal ownership over enslaved people (as opposed to their husband’s ownership), and often won. “For them, slavery was their freedom,” Jones-Rogers observes in her book.

They Were Her Property upends a lot of older scholarship. For example, previous scholars have argued that most southern white women didn’t buy, sell or inflict violence on enslaved people because this was considered improper for them. But Jones-Rogers argues that white women were actually trained to participate from a very young age.

“Their exposure to the slave market is not something that begins in adulthood—it begins in their homes when they’re little girls, sometimes infants, when they’re given enslaved people as gifts,” she says. Citing interviews with formerly enslaved people that the Works Progress Administration—a New Deal agency—conducted in the 1930s, Jones-Rogers shows that part of white children’s training in plantation management involved beating enslaved people.

“It didn’t matter whether the child was large or small,” one woman told the WPA. “They always beat you ’til the blood ran down.”

As adults, white women often tore black women away from their babies so they could nurse the white mistress’ baby instead. To this end, white women placed thousands of advertisements in newspapers looking for enslaved “wet nurses” to feed their own children and created a huge market for enslaved black women who had recently given birth.

Why did these white women want black women to nurse their children? One complained “she felt like continuously having children and continuously nursing her children made her ‘a slave’ to her children—that’s an actual quote,” Jones-Rogers says.

Some black women reported in WPA interviews that their mothers would always give birth around the same time as the white mistress, suggesting that these mistresses were also orchestrating the sexual assault of enslaved women.

“There were instances in which formerly enslaved people did in fact say that their mistresses either sanctioned acts of sexual violence against them that were perpetrated at the hands of white men; or that they orchestrated instances of sexual violence between two enslaved people that they owned, in hopes of producing children from those acts of sexual violence,” Jones-Rogers says.

White women also fought to maintain the wealth and free labor that slavery provided them through the Civil War. As Union troops made their way through the south freeing enslaved people, white women would move enslaved people farther from the soldiers’ path. One woman, Martha Gibbs, even took enslaved people to Texas and forced them to work for her at gunpoint until 1866, a year after slavery’s formal abolition.

After the Civil War, southern white women sought to recreate slavery through exploitative work contracts. Some also wrote books portraying the institution of slavery as gentle and benign—the most famous being Gone With the Wind by Margaret Mitchell, a woman born 35 years after abolition. Yet as Jones-Rogers argues in her book, it was not only white women’s “ideological and sentimental connections” to slavery that made them defend it. Scarlett O'Hara would’ve been protecting her economic interests, too.

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